It only proves that the server isn't storing your original password (since it never receives it). Well designed servers using salts and good password hashing do

It only proves that the server isn't storing your original password (since it never receives it). Well designed servers using salts and good password hashing don't do this anyway (but there are plenty of bad ones out there). It doesn't prove that the server isn't just storing the derived password in plain text (which is all that is needed to log in to this server). And it still doesn't mean that the original password can't be recovered if the password db is compromised.