hmmm, the performance suggests it's not a particularly good implementation of one. (performance at sizes that fit in the cache being lower than performance that exceed it...)

Also the statement in the text is just false ("Radsort is a radix sort and as such unable to adapt to patterns in the data")

MSB absolutely can adjust quite easily. Even LSB can pay some attention. And hybrid like I suggested (use MSB to bucket based on high bits and then LSB) absolutely can...

You are right, a better wording be a "is a pure radix sort".