Accidental Turn On of Replication
As for question 1, I don't think there's any way to know who enabled replication once you've torn it down. Even if it was still up, it'd be difficult (there is a login_name column in syssubscriptions that you might be able to use, for instance). 

Speaking to point the second, the documentation for sp_addpublication says you need either sysadmin or db_owner to enable replication.