Was the full list of heroes supported in theses showmatches? Or was this also restricted to a subset of, say, 15 out of 150 (or whatever that number is)?

The announcers/casters were a bit ambiguous about this, AFAIK they said something like : "the teams agreed on a predefined, balanced list of heroes before the game...", and there was no drafting.

(I'm not native speaker, and I don't know much about Dota2 rules)