It just means you have a slower developing individual. Buff Orpingtons are quicker at developing, but I think this Brahma is slower than the usual. That doesn't mean it is a cockerel, though. Time will tell.
There may be some kind of trick to telling the sex of this breed early, but if so I don't know it. I suspect you'll have to wait until 6+ weeks to get a good idea. These are mixed colors, so that makes it more complicated, too. Watch comb development and color.
It doesn't have silkie feathers-- they are smooth and frizzled. This seems likely to be a hybrid between Silkie and frizzled Cochin bantam.
Too early to tell gender. Keep an eye on the comb. It should stay small for the next few weeks if the chick is a female.
From the website, I think there are only 3 possibilities.
Blue Copper Marans, hatchery quality.
Blue Australorp. Already mentioned.
Blue Star. These are a hybrid between Andalusian male and barred rock female. I think this is a strong possibility.
Blue is a dilution of black, and the color...
It's probably going to take a while longer to know with this one. I don't see any male specific feathering, but the comb and wattles are pretty big for that age. If I had to guess, I'd vote cockerel.
When they're sold by single color varieties then you can be sure they are true Ameraucanas, and not Easter eggers. Cackle has quite a few color varieties. I was surprised to see buff Ameraucana since those aren't very common.