Without pretending to read OP's mind, I don't see anywhere that he said it was the OMT he wanted to write about, just that he wanted to write about shadowing a DO who specialized in it. For all we know, OP wanted to write about observing patient care and the difference a physician can make for patients - which, IMO, is perfect for a personal statement. If he wants to write about OMT, I'd agree it's not appropriate for an MD personal statement, but just writing generally about observations regarding patient care, interactions, etc from shadowing should be fine, particularly if this is the physician that OP has spent the most time shadowing.