I think they could be measuring the wrong thing. While it may be true that the air temperature doesn't change the biology of the virus, air temperature definitely changes human behavior (what activities we do and where we do them).
As I understand it, we don't fully understand why seasonal flu is seasonal. The popular suspects are: A change in behavior of people. The decline in the amount of ultraviolet radiation (that damage or kills the virus). That drier air lowers the body defense against respiratory virus infections. That decomposition rate of viruses occur slower in lower temperatures. And finally the lover levels of vitamin D in colder climates.
Does this study provide any evidence in regard to any of those theories?
On the other hand, it does seem almost guaranteed to be misinterpreted by most news sources.
>though protein denaturing occurred at 51 °C
no need for masks in sauna :)