It's a possibilty, but unless you, or someone else is confident enough to open the PC and check you'll never know for sure.
One of my friends had a lightning stike about 300yrds from his house - onto the raised part of the Wimbledon extension of the District Line nr. Parson's Green. The Lightning hit the rail track, but 'pulsed' up his telephone cable and via his modem fried his Hard drive. So it's possible to have problems even if the lightning is only in the area.
I'd get it checked out properly. He may need a new Modem, or it might just be a re-installation issue.