When a pitching coach starts working with the foundation phase of training it’s usually at the begining of an extended plan that has… further down the road, other “add-on’s” to it.
It sounds to me that your at the start of a series of sessions that first starts with the foundation of you form and posture (legs)… then compliments that instruction with more definitive detail.
Perhaps he sees something that would (could) build your definitions better by using this approach … the one he’s currently showing you.
There are other things to consider here too. Your age, build, physique, attention span, level of compitition that your currently at, the time devoted to show you … whatever, the amount of time you and this coach have together not to mention how often, and so forth.
Also, he could see a certain muscle memory in your current form that he’s trying to correct … and even adapt the positive aspects while working around the less so.
All in all, communications is key to a good coach player relationship. At the beginning of each session he should be explaining how-come-why- and what you should be gaining (getting) out of each session. Also, if at all possible, take video yourself or your family should, so you can run your actions in slow motion … frame by frame., so your pitching coach can say…" Ok, stop the video right here for a moment and let me explain this part…"
But like I said before, communications is key. Talk to your coach and ask questions… even if they seem a bit unusual to you… your pitching coach has probably been there before so don’t be too concerned.
And last but not least, your coach probably takes notes… maybe not while your being coached… but latter on. He’ll probably reference these notes before meeting you for your next session so he can pick up where he left off before and guide him to continue or alter the things that he’s going to cover at that session.