Yes, it's weird in my experience. I've never had a boss ask what I was offered. I've had a few ask if they could counteroffer, but that would be the only reason I'd had for them showing any interest in the amount/benefits/perks on the new job. Did you ask if they are planning a counter? If so, you might want to tell them nicely that it wouldn't be of interest to you if that is the case (it's generally a very bad idea to ever take a counter - you burn the bridge at the other company, and the current company will always be considering you a flight risk/unloyal and may pass you over for things or put you first in line to go in the future).
In your case, I would probably tell in general terms (like I'm getting an almost 10% raise, XYZ perks and benefits) but only if I was on very good terms with the boss.
If it was just a casual work relationship (or you actually don't really like your boss) I'd just say something like a very generous raise salary wise, and better perks and benefits overall and then change the subject to something else like how you're working on transitioning X project to Y coworker and need to check in on some files.
If they press you for more detail, just smile awkwardly and tell them you don't feel comfortable discussing the details as you aren't sure it wouldn't violate a confidentiality clause (some companies do have those).