Why is unresolved reference?

I have two simple python files in the same directory, one of which contains __main__ keyword. I can run it without any problem, but PyCharm indicates in red that 'Unresolved reference ...'.

This seems annoying. See here for detaiils:

https://stackoverflow.com/questions/60999815/cant-run-the-scrip-when-importing-from-the-same-directory-in-pycharm