I don't know how they make their Rudd Rangers. Maybe someone else on here knows what they are based on or what they may have been crossed with. It sounds like something Hoover developed in-house, probably using some version of a Ranger.
They don't mention them being sex links. If they were I think they'd mention that. By 4 weeks the boys should be bigger than the girls. If they are red sex links the boys will be white and the girls red. Photos could be interesting.
Something I've noticed with hatchery dual purpose birds, especially when I get several cockerels. They grow and mature at pretty different rates. Some cockerels are bigger and act more mature at 4 months than others do at 6 months. I think that is just in the nature of hatchery chickens. Breeders carefully match a rooster with one or two hens to get the best bird possible. Hatcheries are more in the mass production business and their prices reflect that. They typically use the pen breeding method where you might have 20 roosters randomly mating with 200 hens. You get a lot of diversity when you do that. That's one of the reasons they do it, they can maintain genetic diversity in the flock for a long time, no need for new stock. But it does give inconsistent results. I suspect this is what you are seeing but it would be nice to know if the boys are white.