"That said I do admit to having a lot of trouble trying to understand why craft that are apparently capable of hypersonic travel would spend hours moseying down the California coast from Catalina to Guadalupe islands."
This is more my point than the true combination of every possible claim. It's more, go beyond arguing about whether something did or did not happen, and consider, what does it imply if it did? People are often too bedazzled by the immediate arguments around what may have happened to consider this argument, but it's a very powerful, simple logical tool that can be useful in resolving those questions.
You tend to get rather silly answers for a lot of this stuff if you take it seriously. Especially when you consider what tech looks like in 2021 and what feasible tech looks like in another 50-100 years, to say nothing of thousands. Aliens with interstellar travel tech but apparently no computers to speak of, no internet, no protein folding projects, no awareness of how useful satellites can be rather than literally flying down, apparent ignorance of how much of the universe isn't on planet earth (there is almost no conceivable resource-based argument for them to be here because everything is more abundant out there with no crazy animals running around bothering you) etc. the whole thing just comes off very silly.
One of the things you don't get crazy answers for is classified, but fully human craft. It just there are humans (military or whatever) with capabilities we don't know. That is not a terribly crazy theory; if you look at the past at how long things stayed classified and extrapolate into the present time, it isn't completely out of the question that the military may have some things that are fully 20-30 years ahead of civilian tech, in very particular branches of development. (I don't think it's plausible that they are uniformly ahead of civilian development by that amount, but it's very plausible to have spikes in very certain areas. We have very significant evidence of the NSA having similar spikes in crypto math.) Combine the possibility of real sightings, with a real experiment to see how people react (we have the entire term "trial balloon" for that, because it's a thing we know humans do), and just a bit of misinterpretation of what's happening by the people watching it, and it's not hard to see this as a very significant possibility.
(In fact, if you study what the military has done to its own people at times, it's not even slightly hard to believe this was a deliberate test of something. Even ignoring the unproveable rumors or what other militaries have done, and skipping the unethical stuff, we know militaries will test and trial things on their own people on a routine basis. Even things as simply as the drills not really labelled "drills" until later are examples.)
And I think people lean way too hard on "but aliens could be incomprehensible!". They are bounded by living in the same universe as us, needing to survive to accomplish any other goal, needing energy and mass resources which are exclusionary (if X is using them Y doesn't get to, and all the subsequent game theory that implies), etc. That doesn't mean that we'll understand them to the n'th degree but it does put some bounds on how "cloud cuckoo land" they can be before it's just absurd.