IMO that means HP was most likely inside the building on the 17th, not *necessarily* on the 28th floor (if already inside the building I'm sure it wouldn't be that much of a challenge to dump the dog out on a floor someone else got on or off the elevator at)...
As we know, she got picked up from there in 2020 sometime..
I'd be curious to see HP's body language in the cctv from behind the building. Does she look concerned, erratic, etc like JW said she looked at the game?
CBSN said she was walking the dog, but I wonder if that means walking with the dog, or taking the dog outside for a walk...