Soo ... to use his own words against him: "There was no mention of choosing a permanent party."
Or in more general way to put it ... We have no idea what this "commitment" is.
You're either purposely being ignorant, or just misunderstanding how English works. Someone specifically asked if you can change your party members throughout the ENTIRE game. He responded with "in the first act, yes, THEN (implying something changes), you'll have to COMMIT (as it, stick with one party)".
