The story only details the sending of a password in plain text. You are right in that this provides no evidence of the password being stored in plain text. It

The story only details the sending of a password in plain text. You are right in that this provides no evidence of the password being stored in plain text. It is equally plausible, without further evidence, that pingdom is merely changing the password (a likely case if the password is not retrievable) and emailing the new password. I tested this with my pingdom account for which I know the password. The email I received contained my password and not a new password. This confirms that pingdom is storing passwords in a retrievable fashion, whether that be plain text or some form of non-one way encryption.