It sounds like the reasonable version of this argument would be "We've been using React with a Rails back end for a while now, and rather than refactor our front end to use Hotwire/Alpine/etc. and be more compatible with the modern Rails paradigm, we'd rather keep our existing front end and move to Next."

Judging from depth of thought in the the actual arguments he's making, I expect that he's deploying to Vercel.