I'm shocked. I always thought that Matt held the majority of the voting shares, and that the board of directors was mostly there as a rubber stamp.

Voting shares and board of directors are two different mechanisms. Just because he holds 80%+ of voting shares, doesn't mean he can control who runs the company. Shareholders can make up (elect/remove) directors on the board, the board decides who can run the company (or other officials). His vote against was likely true, but if the board is 4 seats and he only has one vote, that's 25%.

A lot of this is pretty typical, but what's interesting is what happens next. He could just remove members of the board with his 80%+ control, and build a board that backs him. I assume they have investor agreements that prevent that.