Just seen this.
If I had been in the pub alone, with friends or even with my child, I don't think I would left because of it. Unless the person I was with wanted to, of course.
It does, however, feel unnecessary to potentially offend others in this way, so all in all I think the couple were in the wrong.
This actually reminded me of a time I was at a beach abroad with my daughter, where many women were sunbathing topless as this seemed to be the norm there (tho the beach wasn't advertised specifically as a topless or naturist beach from what I recall.
My daughter expressed no problem being there per se, but when I suggested I might sunbathe topless myself she was strongly anti it (so I didn't).
There was no obvious reason for her to feel like this. We have always shared rooms when we have gone away and I will have got changed in front of her often, she has seen me sleep topless, she will have come in and spoken to me in the bath, etc etc etc. She has no massive problem with seeing my body. She just felt uncomfortable with me getting it out in public, and I respected that.
We don't have to agree with other people's mores in order to go along with them. I am relaxed about nudity and would happily eat in the presence of naked strangers were I called upon to do so. But others wouldn't so they should keep their clothes on.
(Rationally I know you could use this argument to suggest women should never wear short skirts because it offends some people. That view is abhorrent from me. I can't rationally defend why these two cases are different, but I strongly instinctively feel they are )