I'm not a legal expert, but all this seems to check out with US law. Americans need to remember that some of their constitutional rights don't really apply at ports of entry by design. This inconvenient truth for the land of the free has existed for a long time, this situation is just drawing attention to it. Their powers are far-reaching.
Fun fact, there is a long standing exemption to the unreasonable search and seizure protection laws if you're out on a boat (it may only be on the open ocean and Great Lakes, though IANAL). One of the earliest Supreme Court rulings essentially said that without it, it would be impossible for the US to enforce tariffs, which were the main source of revenue at the time. Anybody who boats often enough has been boarded by the coast guard for various safety checks that allows them to poke around and there's little you can do about it.
Any “navigable waters” fall under this jurisdiction which at a minimum includes all salt water and the Great Lakes, plus a few other odds and ends rivers and so forth. Indeed, almost all state and landside federal law goes out the window on a boat - a frequently bumped into example by boaters here in Washington is getting a civil penalty flavored reminder from USCG that cannabis is still (for whatever reasons) federally an illegal substance, and having it on a boat at all is an offense (with larger amounts or future violations escalating as far as seizure of the vessel).
Marine laws are nuts.
Furthermore, "the law" in this area is currently different in different Federal circuit court jurisdictions...
The US / common law jurisdictions typically only have very light self-incrimination protections. The 5th amendment in the US only protects against self-incriminating testimonial. That's it.
In most other jurisdictions (i.e. civil law) it's perfectly legal for the accused to destroy evidence (assuming you're not committing any other crimes in doing so, like breaking and entering, property crime etc.), seizure being ordered or not, while it remains illegal to destroy evidence at the behest of someone else. I.e. civil law usually doesn't criminalize self-protective conduct. That's true even in e.g. Japan.
That's interesting. Where can I read more about this?