I believe he is trying to say their ability to recover from such a large variation from their initial expectation is proof that they truly understand/are advanc

I believe he is trying to say their ability to recover from such a large variation from their initial expectation is proof that they truly understand/are advancing in their knowledge of hypersonic flight. That said, since there is a break between the two quotes the second could have come 10 sentences later and the writer could have unknowingly dropped context/information in some omitted statements. It is a bit of a hard to parse statement, but that is what you get from people, rarely do people speak in memorable, concise sound bites 'off the cuff'.