Customers couldn't get in? You were blocking the door?
I'm sure he was ignorant, but if you were blocking the door, I suspect that he'd be within his legal rights to "ask" you to move. He may not have thought of that, instead relying on his misunderstanding of a different law.
However, courts are increasingly coming down on the side of property owners and individuals and against photographers, so it is difficult to say just what is in fact legal to do with a camera.
If you were shooting with an iphone, he wouldn't have had a problem with you.
No, it is NOT rational.