Maybe colloquially encryption could refer to hashing to a layman, but they are certainly two distinct things. it may been a long while since any password system has used a reversible method, but its also been a long while since sending plain text passwords over email has been a thing. So who knows.
While this is just speculation, I would be almost certain that they are not sending the email without having already stored the information, as that would just be conceptually poor design. You don't want to send off an email saying an account was created when in fact it subsequently had an error saving to the database so does not exist at all. Leaving the user to WTF. But I guess its that poor design vs the poor design of plain text passwords, we don't know what they did.
Either way, of course nothing is unbreakable, but web security isn't about 100% preventing any possible breaches. It's about taking reasonable steps based on the application to keep your ass covered.
