The difference is if you generate a one time use token and send it to the user for limited access to change their password, then you're using a one time use token. Yay, as expected.
The other way is to change the password to a random value and send this to the user. Similar to the one time use token, but your F'n abusing the password system to also act as a one time use token.
It doesn't seem like much of a difference, but it's a slippery slope and easier for mistakes to be had when you mix your authentication logic with your one time use logic. I've seem strange abuses or requests for abuse in my time. Make you cringe.