1. The reports are all second- and third- hand. To my knowledge, no DoD employee has testified to anybody in Congress that they personally witnessed extraterrestrial technology or "biologics".
2. The exception here is a "Jonathan Grey", who hasn't testified before Congress, or, for that matter, been identified; he's one of David Grusch's sources, under a pseudonym.
3. Some of the people testifying believe a lot of other things besides this UFO stuff --- Grusch for instance has peculiar beliefs about interdimensional travel, and is also certain that the Vatican is deeply involved in this cover-up.
4. We know about Grusch's testimony because the Pentagon cleared it, where "it" refers to what would be the single most significant military secret ever held by the government of any country.