It's also obvious that it's a translation blunder; not gonna hunt for it, but the line probably goes something like 一人で寂しいね, which has none of the facepalmy obviousness present in the English line.
Am I just stupid or why does this make sense for me. I mean "alone" and "lonely" don't have the same meaning. As the former is areal and the latter describing the emotion. You can be lonely in a room with many people, too. As you can be alone in a room, but not lonely. ... eh, don't get it. I think I'm thinking too much again.
Well, a more accurate translation of what is being said in the scene would be "Being by yourself is kinda lonely.", which is the same as what we see in the screenshot (because "by yourself" is tantamount to "alone"), but wouldn't appear redundant.
