Like you, I was confused as to this logic, so I did some of my own research. I had been told by a personal trainer that taking a hot shower vs a cold one when it’s 100° outside would cool me off better than taking a cold one. From what I read it has to do with tricking your body into thinking that it is hotter than it actually is. So, drinking hot water or taking a hot shower will increase your core temperature thereby telling your body that it needs to protect itself by cooling down some & the body draws from its own self-defense mechanisms & begins to work to cool itself down some. I’ve never tried drinking something hotter during the summer, but I have taken extremely hot showers to cool down & it worked. IF you take a cold shower, your body thinks that it’s cold & it will work to heat itself up some in order to protect itself from the cold. I don’t like cold showers so I’ve not tested that theory. I was satisfied that since taking the hot shower had succeeded in cooling me down that the opposite was most likely true!!!