That was... Bizarre. Humorous, but bizarre.
Never seen it before myself in any of my games.
If the score had been closer, I would've asked about logic in place for laterals and such at game's end to try and get a tying / winning score, but the game was a bit of a blowout.
A couple of things I did note:
1) After the receiver (WR1 from the Play's Assignments) shed his blocker (CB1?) near the line, the blocker stayed stone still where he was (was supposed to be playing man-to-man). He 'tracked' the QB by keeping him in is field of view, but only started moving back towards his assigned receiver when the ball was thrown.
2) The receiver did break forward momentarily (maybe a yard or so after the catch), with a block thrown in front of him. 2 other defenders (that I could see) were in the vicinity and closing when he turned back.
3) The stats (other than the safety itself) weren't counted. QB didn't have his yardage / completions / attempts adjusted, nor did the receiver get credit for the catch or yardage.
Not sure what else to add... Truly a weird play.