The answer to that would be a big deal depending on what he did in this case.
Are you linked? Yes because you used the same IP.
Is it a big deal? No, not if that is the only linkage factor. As time has gone on and technology has changed I have seen that IP alone is less and less of a doomsday linking factor, at least that has been my personal experience.
IP alone won't so much be an issue, but if you logged into the other acct on the same browser with cookies from the other profile, that would be a hard link you won't be able to get around so easily.