While sending your password in plaintext over email is very much a bad idea and a very bad practice, it doesn't mean they store your password in their database as plaintext.
You're correct and after reading more of the thread I saw OP say this was sent immediately after registering. I don't have reason to believe it is stirred in plaintext unless they're storing s copy of every email they send.
Point is, a hash isn't a password. giving the most you don't need tech knowledge analogy, it's like the passwords fingerprint.
The police station may keep your daughters fingerprint so that if they find a lost child they can recognize it is your daughter beyond any doubt. Your daughters fingerprints, is like a hash, your daughter is a password.
The police should not store your daughter... that's bad practice. The fingerprints are all they should store, and needless to say the fingerprints aren't your daughter, just as a hash isn't a password.