Yeah that's the first thing I saw... back neutral "enough"... butt not very much sticked out. I don't know.
And yeah my stride frequency is very high so one explanation might be good hamstring development. I have no idea if it has any bearing on that though... from what I'm aware of, the hamstrings in a sprint, besides helping into hip extension (ideally) - they prevent knee hyperextension when the leg is swung forward so I have no idea if that's a factor in the stride frequency deal.