It's an old fashioned phrase, based on objectification, that sounds fairly distasteful and a bit creepy.
Yes, calling women and girls 'things' is part of the thousand tiny cuts of sexism in our culture that remind us in a thousand tiny ways daily that we are ornamental second class citizens.
In and of itself it's fairly slight and seems inconsequential, I agree with those posters. No big deal.
If one quantifies and notes every little message that tells a girl that the measure of her is how well her body and appearance measures up to some imaginary requirement of beauty and desirability, that at base she is an object whose worth lies in how <pretty> an object she can be, that she must flirt, primp, starve, abase, simper, pose, pout, giggle, appease, smile, adjust, filter, make-up, fix, check, groom and present herself just to be accepted as worthy of being looked at, we may see why some object to it.
It's fucking relentless and our daughters deserve better.
The last thing tween girls need is a nod to the male gaze on the back of a fitting room door.