President Yanukovych fled to Russia. The office was vacant. The duly elected Rada (the parliament) did what it is supposed to do in those circumstances. They voted to impeach him. His prime minister previously also fled to Russia with the then-vice prime minister becoming acting prime minister.
Following Yanukovych's impeachment the then-chairman of the Rada became the new acting prime minister and the acting president per the 2004 Constitution until the spring elections. Shortly thereafter the Rada voted on a new prime minister.
The interim parliamentary coalition collapsed as planned at the new elections later that year.
That's how Ukraine's laws were supposed to work.
And yes some parts of the coalition were from the far-Right Svoboda. But again that's how it was supposed to work.
Svoboda was already in the Rada as a minority opposition party. The composition of the interim government was voted on by the elected members of the Rada. Svoboda got 3 out of the 18 posts in the cabinet.
Svoboda were big losers in the following elections. They now only have 1 seat in the Rada.