Yes, it is totally a thing. We don't have a lot of hot nights in Denmark but when we do, we still sleep under a duvet, or maybe half under one and it is just as awful as it sounds.
Are you sure? That seems like the sort of thing people might just not do. It can't take that many brain cells for an uncomfortably warm person to work out that more blankets make you more hotter -> less blankets makes you less hotter.
The article seems to provide very limited evidence that people sleep under blankets on hot nights and it sounds like a silly thing to do in the abstract. A lot of people would just remove the blanket when they get hot.
Sleeping with blankets is very comfortable. If the comfort outweighs the discomfort from being mildly hot, it makes sense. Personally I just run fans and/or AC such that I am still comfortable under my blanket, because the price I pay for electricity is worth far less to me than the comfort of sleeping with a blanket.
I sleep with a blanket even when it's too hot. 90% of the year the temperature is low enough that I need it, and sleeping without it the other 10% of the year just feels wrong, and I feel exposed.
The article seems to provide very limited evidence that people sleep under blankets on hot nights and it sounds like a silly thing to do in the abstract. A lot of people would just remove the blanket when they get hot.