Definitely is a pretty strong word when trying to sex a 7 week old bird.So if a chick gets the 3 pea comb at 7 weeks it is definitely a boy even if there are no other Roo signs?
That looks like a pullet to me. Can't see the comb very well, but a developing cockerel comb is usually more prominent and can be seen in profile. A close up of the comb might help confirm things.