Engine Fault 3rd to 4th??

So redlining in 3rd gear, I went to shift to 4th, let the clutch out a little too fast and hit the syncros hard. Hit the gas, and the engine revved way over the rev limiter and an instant engine fault popped up. Airbag light went off, and traction got turned off. Engine went into limp mode, and as soon as I turned it off and turned it back on, everything was alright. This happened twice so far and I've definitely learned my lesson.

I'm just confused as to how the revs could've went up so high when I wasn't actually in gear? I'm 99% sure I didn't hit 2nd by mistake and both times the shifter was just in neutral. Hopefully I didn't cause any damage.