So I translated it back into Ukrainian, and it looks like this:
Вони загинули, бо стали на захист чоловіків і жінок, дітей і літніх людей, які опинилися перед загрозою винищення інтервентами і оплаченими ними нелюдами.It is somewhat complicated to parse what happened here. Yats speaks fluent English, but I doubt he gave this statement in English. More likely, he did so in Ukrainian, as the statement is in regards to the apparent shoot down of a Ukrainian troop transport plane near Lugansk, in which forty or fifty troops and crew were killed. It's a statement of revenge on the Russians and the rebels for their temerity -- assuming the plane was shot down and it didn't crash for other reasons the way these things sometimes happen.
When translated at the site from Ukrainian into English (there's a little button in the upper right corner that lets the reader switch between Ukrainian and English) the term нелюдами (nelyudamy) is rendered as "subhumans", but my balky offsite online translator renders it in Ukrainian as "fiends" and/or "monsters."
In Russian, however, the term is rendered as "non-humans." On the other hand, the sentence as a whole is complete gibberish in Russian, and the isolated word comes out "unsociable" in the context of the gibberish of the rest of the sentence.
I tried a German translation, and the term was rendered as monster or fiend, not "subhuman" or untermenschen.
So, where did it come from? Who knows? More than likely, the translation of the term нелюдами as "subhumans" was done as a deliberate provocation. It seems to have worked.