But that's what he said. Scientists don't believe in magic or the supernatural, thus in this context they use the phrase "known laws of physics", rather than simply "laws of physics", because it is an obvious truism that nothing could ever violate the actual laws of physics.
Scientists avoid the word "alien" when possible because it's casual and has multiple meanings, "offworld" is much clearer. And if he used "UFO" or "UAP" in this context, you could easily claim that those are the wiggle words, because if the government had identified the craft then it wouldn't be UFO/UAP anymore, would it?