No, this does not indicate whether they are storing your password in plain text or with reversible encryption. They might be, but this still leaves other possibilities open. All you know for certain is that they created a new password and emailed that new password to you. That password may well be hashed appropriately for storage in their system.
However; this is a poor security practice and I would absolutely gripe to them about it, and point out that such a poor practice in one regard makes you suspicious of the quality of their security practices in other regards.
Email is not secure, and they shouldn't be doing password resets by sending you a new password in any form, anyway.
I just installed an open source file transfer application on one of our servers to check it out.
I confirmed that it is hashing passwords for storage in the database, which increased my comfort level. Then I created a couple of accounts and realized that the stoopid thing emails the passwords at the moment of account creation in plaintext to the new account holder.
I am beside myself. One of these was actually a fairly sensitive account, for which the account holder should absolutely not have to change the password (but will now be forced to do).
This utterly stupid, utterly non-secure nonsense has got to stop. A plaintext password should simply never, ever, under any circumstances EVER be emailed. Ever. End of discussion. That entire mode of thinking should be quashed instantly whenever it is encountered, and public websites that engage is such practices should be punished for it.
They should be doing password resets by sending you something like a reset link with a (long, complex) embedded code/token, which permits you to choose your own new password, over a secure (HTTPS) connection. Ideally, upon clicking that link, you would still be required to answer another security question or two, in order to confirm your identity. Or some kind of 2FA should be implemented, where you click the link, then you have to punch in a code that was texted to your phone. And I still feel that you should have to answer at least one more security question on top of that, because 2FA is still utterly susceptible to having your phone stolen or cloned.
That reset link should have a very short valid lifetime. In my opinion, it shouldn't work for more than about 5 to 15 minutes. If you don't get around to changing your password in that time frame, you can always request a new link when you're ready.
If you ever encounter a site or service that sends you your existing password in plaintext, then you must assume they're storing it in plaintext or using reversible encryption.