It was the middle part between the two bits you quoted - he was just going to a show, was in a phase where he liked wearing all black, and would get waved in without even intentionally trying to trick anyone because they assumed he was arriving for work. Does that help?

I didn’t interpret “show up” as having purchased tickets and planned to enter, rather unintentionally get let in as was their implication.

Show up can just mean arrive, no implication one way or the other.

Yeah. These would all have been "show up and pay at the door" type places, not sold out weeks in advance with pre-booked tickets. Bouncer (or sometimes door bitch) takes your money, unless the bouncer waves you through.