Unfortunately that confusion starts in excel documentation, it's a mess in the case or the word Blank.
There is a terminology error in the the excel documentation that makes this problem confusing: the word Blank is used with 2 different meanings.
The 2 different meanings of the word Blank in the help:
1 - A Blank cell can mean an empty cell. This is the case with the function IsBlank() and the Paste Special with Skip Blanks
2 - A Blank cell can mean an empty cell or a cell with a null string. This is the case with the function CountBlank() and in the Autofilter when you select Blanks in the dropdown
This means that it is always confusing if one uses the term Blank. Maybe the best would be to avoid it and use instead for ex. "empty" or "empty or with a null string".