What was wrong with this pigeon?

This was a few years ago but I sometimes think back to it. I went outside with my family and there was a pigeon in the town centre which wouldn't be unusual if it was completely "zoned out". We don't get many pigeon-feeders in this area but this one was completely oblivious to people getting super close to it whereas more friendly pigeons would still be scared - it walked around a little and ended up staring at a tree, completely still. Some other people were also confused but nobody wanted to go too close. We went to a restaurant and when we came out, it was sheltering from the rain right next to the restaurant door, still blankly staring forward.

What was with this pigeon? My first thought was rabies, but I found out that birds cannot get it, so I'm completely lost as to what was with this pigeon. Unfortunately, we could not take it in so I don't know what happened to it afterwards