If it's not strange for your boss (as you know him) then I'd have no issue with it. But personally, in my own work, I'd find the situation odd. Not the compliment from the other girl, and even if it was any other male while I was at work with a passing "Hey, you look good today!" I'd love the compliment

But to get a text after work, and as Rouge said apologising and using the word stunning, it seems like he's thinking about it maybe too much, and I don't see the point of going to the effort after that matter to kind of go out of your way to say you looked good today.

Not sure I've made much sense there, but it just seems a bit out of the ordinary to me.