They were 'joint' because the Ukraine used a test range in Crimea that belongs to Russian Black Sea fleet based in Sevastopol. All launches were authorized by Ukrainians, Russians fired a single short-range missile and that's it. But, yeah, let's call it joint Russian-Ukrainian to shift the blame towards Russians.

You can read the details here using google translate if you like: https://ru.wikipedia.org/wiki/Катастрофа_Ту-154_над_Чёрным_м...