Divine I think it's probably as you describe. It is a little odd, but he feels the day we actually got together is massive for him so he wants to mark it.

He knows I detest surprises so it's unlikely but not impossible that he would go over the top.
However he has also tried to insist that everyone loves good surprises. I have assured him NO surprise is a good surprise as far as I am concerned.

I guess it doesn't really matter, it's just a day, and if it's important to him it's no skin off my nose. To let him have it.

(UPDATE)
He is sick as a dog...lol, poor bstrd!
Looks like I will be spending the day serving soup and fruit juice.