I feel as if it truly is a legitimate English sentence. But it doesn't really help you understand what the translation really means. For instance, Do the Indonesians view a "plus size" shirt as a "wide" shirt? Or do they really mean to simply remark that the literal width of the shirt is noteworthy somehow? Either way, I think either this statement or its translation should be changed to clarify all these reasonable complaints.
As noted by others, this English translation is totally meaningless.
But more frustrating is that hovering over the word 'lebar' gives two definitions in English, one of which is large. Despite offering 'large' as a translation for 'lebar', duolingo still aren't accepting 'That shirt is large' which, of course, is a readily comprehensible sentence in English.