Comes from 'eeproms' (Electrically Eraseable Programmable Read Only Memory) units in days of yore which were 'flashed' so they could be written on again. Typically, a computer geek would understand this usage.
Technician: "Make sure you flash the drive first, for security reasons."
PC Onwer: "WTF?"
Tech: "Uhh...erase all the information."
Dude: I dunno, must have been the flash.