It might be because it was the only one standing, but the first one's legs seem very long which can be an early indicator of a roo. Barred rocks are usually sexed at day 1 by their color patterns but at 10 weeks it isn't always easy. In my opinion number 1 looks like a cockerel and number 3 looks like a pullet. If you don't want to feed potential roosters you might want to rehome them now. You could alway wait and when you know you will know. Good luck!