I think the idea of “martial race” is plain nonsensical. The Sikhs empire was actually defeated by Caranatic Pandey soldiers serving in the British army who weren’t a martial race at all. Never had any martial tradition or history of warfare.
An uneducated guess is that the ‘martial race’ concept was an H.R practise of the medieval era for the Brits to boost their colonial military. A community with a culture of sending men to combat had the military as a prime occupation and trained up its youth for the role.
Many of the ethnic groups which were thus designated-Gurkhas and other hill communities, Jats, Sikhs and Pathans still figure prominently as far as numbers go in their respective armed forces.