But not all birds have hollow bones, or even just hollow bones.
For example, penguins have solid bones. Ostriches have solid bones in their legs, but the rest are mostly hollow.
As a flightless bird with a humanoid shape, I would speculate that kenku have solid bones so that way they have the body strength to even wear armor, or pick up heavy weapons.
So while Jubilant Black Gale might be a buck fifty soaking wet and light for an animal his size, he'd still be able to carry his equipment with breaking himself.