You are not entirely right. In python, one line means something as it is only one statement (as mentioned above). Author is also strict about not using eval -- with eval you could snuck multiple lines into one line (using \n in the evaluated string).
Last time when I used python I could separate statements with a semicolon and put as many as i want in a line. Did that change ? ;-)
This did not change, but the author also didn't use semicolons. As stated many times above, this is a single Python expression.
I'm not sure you can write function definitions, (nested) loops and other things that rely on indentation in single line using semicolons. At least I never managed to do that.
I reckon that the challenge involved in reducing the problem to one line (as in one single Python statement) has little to do with how many characters long it is.