There's a more benign answer to the creepy connection suggestions. LOTS of people import their email address books into linkedin. It's not a stretch to think that his girlfriend's mother (or some other relative) imported her address book that contained the names of both the OP and the girlfriend's stepfather.
As far as the creepier name mismatches go, my oldest email address list has tons of maiden names and unused/defunct email addresses. It's likely that some high school friend of the OP uploaded an old address book and LinkedIn's algorithm made a best effort match on some of the rarer names even if the email addresses don't match. I mean, how many Lucy Hatsbaughs do you think there are on linked in? Two? LinkedIn may as well gamble on odds like that.
As far as the creepier name mismatches go, my oldest email address list has tons of maiden names and unused/defunct email addresses. It's likely that some high school friend of the OP uploaded an old address book and LinkedIn's algorithm made a best effort match on some of the rarer names even if the email addresses don't match. I mean, how many Lucy Hatsbaughs do you think there are on linked in? Two? LinkedIn may as well gamble on odds like that.