Judging from video, the An-26 was shot down at altitude about 4400 m, not 6000 or more (perhaps claimed by crew). Also, its engine was hit, therefore IR homing. Buk has radar homing.

You left out the bit how most of those transmissions were on military-only UHF, and the other transmissions were vague and non specific. At least the crew of the ship had the capability to warn them. Who knows, there might have been circumstances where the missile launcher crew genuinely believed they were a threat? Maybe one the crew had failed to fire an a target before believing they were a civilian aircraft and it turned out it was a military aircraft? Human factors played a part in IR655 and they probably played a part in this one too. It may be that they never come to light though.

The reports I read said it was at 6500 metres. It was a Russian media outlet (TV Zvezda) that said it was a BUK that did it. They said the rebels had captured a BUK from Ukrainian forces. A claim we now know is nonsense. The launcher was supplied from over the border as the photographic and phone footage evidence shows.

Still, even if it wasn't a BUK (which I think it was) it proved that the rebels had a game-changer on their hands.

This, I think, shows up the culpability of Kiev for not closing the obviously dangerous airspace and the airlines that chose to continue to fly over the war zone despite the changed circumstances.