My response to that would have probably been silence, just like your friend's.
I had a somewhat similar experience at a party I had. During the party, several people were making presentations (the details of this aren't important) and we were just about to take a break before continuing. Up jumps one of my guests, bounding to the front of the room, and with a flourish, she announces she's lost x pounds (can't remember now, how much... 30 maybe?) and doesn't she look great?
I was dumbfounded and I think most of my other guests were too. What an awkward moment. To top it off, I had also recently lost quite a bit of weight (more than she) and had gotten compliments on my looks -- in private conversations. I wouldn't have dreamed of making a public announcement like that and asking for kudos!
But you know, some people!