What frequency of echo, alt, speed, modulation?
Even SA-11 can separate targets by onboard soviet computer by type - aerodynamic target, aeroballistic and hover/low speed.
It possible by analising of modulation of signal from target by parts of plane, number of engines and rotating parts in it. Qualified personnel can hear difference between targets and even what maneurs target can do.
And i dont talk about acquisition of target on radar... Farina&Studer for who wanna understand how radar plot track on screen.
Su-25 can climb on 10k meters, but airspeed will be much lesser then MH17 speed.
Holes in roof of cabin mean plane with gun had alt more then 10k m. Then this atacker must be shown on Dnipro and Rostov radars (since Rostov radar seen Su-25 on alt=5000m). Also Su-25 altimetr dont have ability for show alt more then 10k m.
About Buk missile which can fly dozen miles after detonating:
At end of video falling aft part of missile, how you can see it cannot fly, but can fall.