So I'd say that's probably what happened here (i.e p was reported composite by a randomized primality test and that would never have happened had it been prime).
Oh sure, I don't mean that there's uncertainty that this number is composite, just that in a formal sense there isn't "proof" that other numbers that passed, say, openssl -checks 100000 are prime. But I wouldn't consider it unsafe to use them for cryptography.
The comment I was replying to referred to tests that "tell you if a number is prime or not", and the probable ones don't exactly always do that. :-)
So I'd say that's probably what happened here (i.e p was reported composite by a randomized primality test and that would never have happened had it been prime).