sudo gives you root permissions. It does not change your user to root.
ok, I ran
-rw-r--r-- 1 root root 785 Dec 28 15:44 authorized_keys
so it would seem that su makes you root and sudo adds you to the root group (for the duration of the command), which confirms what you are saying.
Thanks for the help, I've seen quite a few discussions/articles on su vs sudo but I've never seen anyone mention this difference. I will watch out for that in future.