This is actually not using a chess engine at all.
Meep has an MTCS (Monte-Carlo Tree Search) framework, so the entire AI here is just a set of chess rules plus a state heuristic.
Basically it can play any turn-based game, as long as you can describe what the rules are and define the victory state.
I wrote it many years ago, following the success of Google’s Alpha-Go, and used it quite successfully in Might is Right for combat AI. Even though the combat itself is relatively simplistic in that game, the strategy during combat is quite deep and there are probably billions of possible squad combinations with all the unit classes, equipment and talents.
I thought that chess might be a nice way to demonstrate the capability of this tech in meep.