It is confusing and I don’t think they can adequately cover it in a press release.
I think it all depends on what point in time you begin the discussion. For this they start at a time of relatively warm temperatures, worldwide.
My puny speculation is that there may have been times when the planet as a whole was warmer or cooler but probably more times when global temperatures were distributed more and less evenly.
They mention less ocean circulation. From that I imagine colder waters more staying deep and warmer waters more staying on the surface. If that imagining should be correct then the entire surface of the planet would have been warmer.
And there you have some speculation from a rank amateur. :-)
I can’t remember where I read that as long as our continents are where they are in the Northern Hemisphere, all crowded around the north pole, we are stuck in cycles of glaciation. The continents keep the water from easily circumnavigating the globe.
I’m not an expert, and I don’t play one on TV.