I don't buy it for a minute. You can leave an uncovered EPROM in direct sunlight for a week, and the data will probably survive.
I'd suspect a localized "EMP" transient from the camera flash before I'd suspect an erased EPROM. It takes a lot of energy, in the E=hv sense, to erase an EPROM.
Believe it: windowed EPROMS have been used as cameras. Their light sensitivity is legend.
[edit] actually I was wrong about that. The memory devices used as cameras were delidded RAMs, not EPROM. EPROMs are light sensitive, but too slow for that.
I'd suspect a localized "EMP" transient from the camera flash before I'd suspect an erased EPROM. It takes a lot of energy, in the E=hv sense, to erase an EPROM.