As usual, it's called: error in speech / misspeaking. Everybody experiences one, even in important events. Since Chapin passed away 4 years ago, exactly in July 4, I think that's why he misspoke "days ago", since the upload date is July 30.
Mangini has so many pieces in the drum kit, he doesn't have to make unnecessary reaches to other pieces in the kit (and no duck face). You can't judge his playing solely by perceiving it visually, use more of your ears and musical thinking.
Portnoy is all about RLRLKK RLKK RLRLKK, Mangini's more than that: polyrhythms, limb independence, dynamics, and their buddies. Check out Mangini's clinics and other performances, don't just judge him based on his DT performances and advocate other's opinion.
Since he said 24 limb pairs, it means he has 48 actually.
Check out "The Enemy Inside". In fact, that's just from the self-titled album where Mangini composes within the making. It's his first time composing, not in ADTOE.
The other DT dudes just composed the drum parts for Mangini in ADTOE due to his absence and some auditioning yet to come at that time.