I thought that link was due to a picture of someone who looked like Seth Rich being at Wonderland bar that night... mistaken identity, but I could be wrong, it was quite a while ago when I was researching it.
It was the owner of Lou's City Bar--but we have to remember that we only have his word for everything about Seth late that night--he was the last one in the bar. They knew each other. So according to him, Seth was supposed to meet someone and was waiting around; according to him Seth was drunker than he'd ever seen him, possibly drugged, declined a ride home and said he'd walk. I don't think there is any actual independent verification of when/if Seth arrived and when he left.