I don't understand why people give this reason. Your PB ao5 is the fastest ao5 you ever did, right? And that's looking at any consecutive 5 out of all those 1000s of solves you did? You'd need a lot of luck to repeat that in a real (not fantasy) competition. If you sit down now and just do 5 solves, your result is much more likely to be somewhere in the region of your global average, so that's a better indicator of your real (not fantasy) level.
It can happen of course. I got overall PB ao5 in 5x5 at my last comp, but it was freak good form and luck, and I would not claim that's my actual level. Usually I am 10-15 seconds slower.