Quite frankly, I don't see the issue with meeting elsewhere to buy/sell a bike, or anything else.
I have twice sold bikes meeting the buyer in a public space. Reason, I don't really want people knowing my address or inviting random people into my home (don't forget a buyer can be a sketchy character as well as a seller), I want to sell them a bike, be paid and that is that. I meet them in a public place, eg. outside of the nearest train station or uni building so that it is a safe place (well as safe as can be) for both parties, with CCTV camera's and plenty of human traffic make the sale then part ways. No big deal! That being said, I also hand over full documentation at the same time!
This seller does seem a bit sketchy to me, so you might have done well to walk away, but that's life!