Between his browser being used (it would have a fingerprint logged as "trusted"), a password, his home IP, and OTPs being sent to his phone, I can see why they aren't in a rush to cover it. That's a lot of things lining up at once.
Of course, there could be a combo of a pwned computer and a sim swap, but that's a lot of trouble to go to for $15k. Not unheard of, but there needs to be a lot more than just his word for it at this point.