Oh, I did terribly. Probably 3-5K. You're right about the machine. It was very well done.
I was in line when a guy got up to 50 some K, so they ended up handing shirts out to everyone in line.
The guy who was in front was a douche. Everyone behind him kept saying "just get to 8000 and get your shirt, then move on" and finally he ended and said "I only quit because I was bored"
I saw him around the show a few more times, his attitude just seemed bad.
Not likely to be MAME - that would be an extra (unnecessary) layer of indirection.
Remember that MAME is an emulator - if you are writing something genuinely new, especially for a one-off like this, you wouldn't want to spend the time programming to old hardware just to emulate it.
Might well be a PC running their custom program full screen (that would be a pretty quick environment to program the game in).
If I were going to build something like that, depending on time constraints, I'd probably use an embedded Linux board (there's lots of ARM boards out there for reasonable prices). Since the graphics, etc, aren't that complex, you'd have no trouble keeping up with it on such a platform, and you would avoid all the usual shenanigans with getting PCs to do stuff in an embedded situation.