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.
It's possible that this email is a result of forum user creation, so during that submission the plaintext password was available to send to the user. Then it would be hashed and stored.
I'm just explaining how user authentication works for most web applications. The server will process your plaintext password when your account is created. It should then store that as a hashed string, but it can ALSO send out an email with that plaintext password to the user describing their account creation. This post does not identify that passwords are stored in plaintext, it just identifies that they email plaintext passwords which is poor security practice.
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.