No it is not Mach 10. Closing velocity was 10.5 Kms/ second. If I remember right satellite was at 7.5 Kms/ sec and ASAT at 3 Kms/ sec.
Satellite speed should be easily calculable based on orbital height.
GEO sats "travel" at around 3.3 Kms / second making them " stationary" to the ground track...