Why are they not engaged custard?
Is it because they haven't done the 'ring - tick'?
And he didn't actually have a big day planned. He told OP he wanted to propose 'soon'. OP was going to wait until the end of February before mentioning it again but lots of posters were suggesting Valentine's Day as the obvious time.
He didn't even want to get the ring, he wanted to go shopping to 'just look'. He is not treating her as an adult with equal say in the matter, that's the problem
She asked him, he said yes. They are engaged, ring or not.
I agree with the idea of just accepting the ring, calmly and politely but just putting it to one side and carrying on with your conversation. He is expecting the big 'oooh, a ring! A proposal, an actual proposal for me!! I can't believe it!'
Don't give him the satisfaction.
Personally, I would really have to tell him how disappointed I was and I would definitely be having second thoughts.
And if you do go ahead with it, put your foot down about the big ceremony. Just imagine what a nightmare that is going to be, trying to organise something you don't actually want with no interest from him.
He's all for show isn't he?