Hopefully the muay thai footwork isn't "incorporated" into the hsing yi and tai chi. Both styles techniques are foundationally laid on their footwork.
I've never seen any mantis footwork that couldn't be found in my tai qi except shape steps, however that's translated, and stuff like that. For a younger person, doing those low walking drills will give you mean kicks and crisp jumping skills. If that's what he's up to, sounds brilliant to me.
If he's teaching you muay thai footwork in free fighting or something though, that's cool. My father in law teaches muay thai, it's really cool, they spend a huge amount of time hitting actual people that hit back, go figure right :P
Ask a lot of questions, it will be good for you, and good for him to remember answers.
"Siezing oppurtunities causes them to multiply" Sun Tze