Frozen liquid items are allowed through the checkpoint as long as they are frozen solid when presented for screening. If frozen liquid items are partially melted, slushy, or have any liquid at the bottom of the container, they must meet 3-1-1 liquids requirements
It is probably intended for ice packs for things like insulin, but worded vaguely to allow ice in a ziplock bag or a frozen water bottle in place of an ice pack. Most of these rules would benefit massively from stating the purpose of the rule too.
https://www.tsa.gov/travel/security-screening/whatcanibring/items/ice
For the lazy:
I would imagine that this is for transportation of medicine that needs to be kept cold like insulin?
It is probably intended for ice packs for things like insulin, but worded vaguely to allow ice in a ziplock bag or a frozen water bottle in place of an ice pack. Most of these rules would benefit massively from stating the purpose of the rule too.
You forgot the most important part: