Ignoring we’re even talking about computers, I read the word ‘maximise' to mean as big as possible. Even if we take your definition it’s still worong.Because that is what maximize is: make the window big enough to fit all content. Otherwise it should read 'fill screen'.
Open text edit on a system that runs the old way. Type 4 lines of text. The window expands to more than the size needed for those 4 lines.