I agree that it is inappropriate for the boy to comment, but not for the same reason. It is just unmenschlech poor manners to comment negatively about her appearance to someone (likewise, for the girl to comment about HIS appearance). There will always come along another young man who likes her wearing those shoes.
BTW, I personally detest the spike heel look. It’s not pretty IMO, it’s totally awful for the Achilles tendon AND sacroiliac, and lethal during simcha dancing at a chasunah. I do like the look of some type of dressy heel, but up to two inches can give that pretty look without being outrageous. Just an observation…