All silicon is photosensitive to some extent. The power supply will be one of the few chips which is primarily "analog"; in particular it will have a bandgap voltage reference. That's exactly the sort of thing to be badly affected by a charge pulse from the flash. Glitching the power supply will then destabilise the digital logic it's powering.
The real question is how the light manages to get through the epoxy casing.
Yes, but if you were tasked with designing the epoxy that was going to be used in every IC everywhere, I would hope that you would go through the extra effort of adding dyes that were specifically opaque to UV and IR.
The real question is how the light manages to get through the epoxy casing.