I've seen this happen at other Pro Shops before. Unfortunately a situation like this helps no one in the end.
For yourself, you would have lost a good hang out, a place to shoot the breeze, hear what other bow hunters have to say, enjoy all the great hunting 'stories' and all that goes onwhen passing the time in a Pro shop.
I'm thinking, even though as you mentioned, the Pro Shop had the chance to carry your strings & cables and chose not to,for whatever the reason or purpose.
This guy probablyfeels, you're using his shop, meeting his customersand finding business for yourself and he's not getting a piece of the pie.
I'm not saying this is the case, but in the cases that I knew of, relating to other Pro Shops--when something like this happens--this is what turns out to be the problem, sometimes.
Even though he sounds 'forked tongued'--- if it's worth your while and you want to stick around the shop--you may think of offering him 'something'
on the strings you sell to customers you met while hanging at the shop.
This kind of shows your willingness to give and take and maybe this is what he's looking for. Some form of commission.
The ball is in your court, I think it can be a win/win situation for both of you, if you can work something out between yourselves.