You’re right about a Russia/NATO war being unwinnable for Russia. Even the current military of Europe alone would be enough to see off Russia.
So, what is he warning us about? I see two (not exclusive) things he could be doing.
Trump winning in America would cause such stress on NATO it would fragment, and even if they kick America out it still looks weak so they want all of Europe to beat the 2% requirement to try and keep trump’s USA in NATO.
Second, he’s warning of war with china. This is where my money is.