The main point of the article was that the Hittite spoke an IE language (evidence from their cuneiform writing), but their DNA doesn't have any Yamnaya ancestry. So, two conflicting points. What the article describes is that they have found an ancient population which they call "the Caucasus Lower Volga people", and their DNA is present in the Yamnaya AND the Hittites, as I understand it. So the hypothesis is that these people spoke an early proto-IE language, and some of them migrated to where the Hittites originated, and others moved west and intermixed with a small region in what is today the southern part of Ukraine, and in a few villages of a few thousand people a whole new economy was developed and this is what eventually spread out as the "steppe migration", bringing proto-IE with them.
So, the base of the article is that they found a population which appears to be ancestral to both the Yamnaya and the Hittites, and that the latter split off before that population became the Yamnaya by migrating elsewhere and merge with people there. What's missing is definite proof that the "Caucasus Lower Volga" people actually spoke proto-proto-IE, but if they didn't then things look even more complex. If they did it would match the current linguistic and DNA evidence pretty well.
So, the base of the article is that they found a population which appears to be ancestral to both the Yamnaya and the Hittites, and that the latter split off before that population became the Yamnaya by migrating elsewhere and merge with people there. What's missing is definite proof that the "Caucasus Lower Volga" people actually spoke proto-proto-IE, but if they didn't then things look even more complex. If they did it would match the current linguistic and DNA evidence pretty well.