How I read it is that they know what your Facebook and Google are, but cannot access them because Wattpad does not process or store your passwords for Google and Facebook.
Or did it somehow gain access to the ID of every online account we have that shares the email address
You are correct - that (afaik) isn’t possible. It’s only what you used for Wattpad. They have no idea what services (i.e. banks, school, etc.) your e-mail is attached to. No doubt, they’ll try to find out by using your Wattpad e-mail and password on other websites you might use (like, as mentioned earlier, banks or other social media).
So yea, if you haven’t changed your password yet guys, change it now! If you’re waiting for a reset link, Wattpad has said that depending on the volume of requests, it may take up to 24-hours for the link to be sent.
Also, invest in a password manager! A password manager like LastPass can be a life savior because it allows you to have unique passwords for every account and you don’t have to remember them! All you have to do is remember your unique password for the password manager. And they usually have the abiltiy to automatically generate a secure password for you.