From this distance, I cannot say what was and was not the
earthing path. For example, you may consider concrete
non-conductive. But to lightning, concrete is conductive.
Same could even apply to wall that camera was mounted on.
Incoming on camera network port, through network interface IC,
then to ground via camera mounting screws.

A most typical reason for damage is incoming on AC mains,
into computer motherboard, through modem, and out to earth via
telco installed (for free) 'whole house' protector. Nothing
in motherboard is damaged even though motherboard is in that
path. A most common damage is modem's off hook relay driver
(PNP) transistor. Path that includes an electrical connection
from relay coil to relay wiper. Yes, those electrical parts
(normally considered separate) inside relay are connected
together during the destructive transient.

In your case, let's ask a few questions. That network card
is galvanically isolated. The network cable is electrically
(galvanically) isolated from NIC electronics by a
transformer. And yet that transformer still connected the
transient into NIC. Again, appreciate what one might not
consider connected is indeed connected via paths previously
unknown to the human.

Lightning is not capricious. But it does find paths
previously unknown to humans who must learn from the damage.
A classic example of 'best evidence is the dead body'.

It is possible for a TV and VCR, side by side and
interconnected, to both suffer the same lightning strike. And
yet only one is damaged - the other remains fully functional.
Why? Again, a path from incoming lightning to earth ground
must first be learned.

Even a mouse wire dangling behind desk on baseboard heater
could become, to lightning, a direct connection to earth
ground. So many paths exist which is why protection inside a
building is so complicated and often so futile. Best
protection earths transients before they can enter a building.

If we built homes to protect transistors, then rebar inside
the concrete footings would be the most critical component of
a lightning protection system. It's called Ufer grounding -
originally pioneered to protect ammunition from direct
lightning strikes. That building Ufer ground would provide
the single point earth ground and act as a halo ground; making
earth beneath the entire building equipotential. But since we
still don't plan for transistor protection, then it is
essential for all incoming utility wires to be earthed at a
single point. That earthing be the best earth ground
available. That earthing makes it unnecessary for lightning
to seek earth ground inside a building through household
appliances.

To get through the NIC, there must be a path incoming that
entered and left NIC on network cable and computer ground.
Since whole house grounding was not utilized, then lightning
overwhelmed a typically 2000 volt NIC protection.

One example of a protection system that uses multiple
earthing methods for even better protection is page 14 at:
http://www.leminstruments.com/pdf/LEGP.pdf

Do we need protection that extensive. No. Even an earth
ground rod at the service entrance provides a massive increase
in protection. High reliability facilities add all that
extra earthing just for a little better protection.

Another example is
http://www.epri-peac.com/tutorials/sol01tut.html . Assume a
transient enters on phone line. Now telephone line protector
(NID) connects to building single point ground via cold water
pipe. But pipes may be too long, have solder joints, etc.
IOW connection to earth is not sufficient. Therefore the
transient also seeks earth ground, destructively, via FAX
machine.

Just some examples of how damage can result if transient is
not earthed before entering a building - the importance of a
single point earth ground.

Dave Liquorice wrote:
The surge was induced in a few metres of network cable and found its
way to ground through the PCs earthed chassis, after frying the
decoupling Cs and blacking the board a bit. It also took out the
network side of the connected IP camera, but without visible damage,
the camera isn't earthed. That was the only damage, the camera still
worked (on it's serial interface) and the PC suffered no damage
neither did the modem connected to the phone line and PC or the modem
connected to the camera and phone line. Nothing else in the house
suffered. Oh and remember the strike was a couple of hundred yards up
the road.

Please explain how "whole house" protection would have protected this
NIC?