Without wishing to be overly provocative, what is sprinting other than a series of alternative single-leg impulses, so you can see why some coaches think derivative squats such as single-leg movements are appropriate.
Personally I think single-leg unloaded squats are probably related more to core-strength and stability than actual leg strength.
I coached a young woman who could do 10x single-leg deep squats off each leg (with the other leg triple extended in front but not touching the ground) but she was hopeless doing double-foot squat with a barbell.
On the other hand, I had the chance to work briefly with a footballer who squatted 246kg but could not do one rep unloaded single-leg squat. He could go down, but could not stand back up.