I love how everyone here is like "hur hur, Elon is a moron" (and of course he is).
But in the end they're just talking around each other. And are both right it seems.
The number of atoms in the universe is about 10^80. The number of possible games (which the chess.com guy was talking about) was once estimated to be about 10^120 (so 40 magnitudes larger). The number of possible positions is currently estimated at about 10^40 positions (so about 40 magnitudes smaller).
In the end i'd say positions is more important in solve a game than ways to get to those positions. For each position you need to know the perfect next move.
But Elon not noticing he's talking about something different than the Chess.com guy is... intriguing XD.