I'm not saying its not screwed up, and I'm sure some enums would be interesting, but they are using it in a logical context so I feel like the ! makes a fair amount of sense.

I do wonder what would have happened if truth had been defined like it is in Forth[1]? That would make me go with the enums.

1) False is 0 (all bits set to 0), and True is -1 (all bits set to 1 giving a twos-complement -1).