Do you do a lot of trademark litigation work? (I'm asking because there are people on HN who are professionally familiar with this subject.)
I'm also not a lawyer but it also sounds not sound. The "enforcement" of the WordPress trademark is so completely chaotic that it seems clear Matt is just using it as a weapon to extort companies he thinks he's entitled to.
WPEngine may very well be doing something wrong, but WordPress needs a clearer license with which to attack them with