It says the Buk that was used to shoot down the aircraft was from a unit that was based in Kursk, Russia. It didn't say the shot came from Russia, nor did it say Russian troops fired the missile.
The Buk missile was fired by pro-Russian rebels in the town of Pervomaisky, which is in the Ukraine, just west of the Russian border.
Russia certainly played a role in giving the Buk to the rebels, but it wasn't fired by Russian troops or from within Russia according to the investigations that have occurred since.
Do not take this as support for Putin/Russia. It is not. It is simply repeating what the investigations to date have stated.
A list of the investigations and results (including today's finding) is located here: https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_17
Very doubtful.
The folks in the area with BUK systems and the training in how to use them were Ukrainian military units.