I think the progress part is about having a common language, not about this common language being English.
If the common language was wolof, people moving back to their own (Spanish, French, German, whatever) would be regression, as now a discussion between French, Spanish and German people would be much much harder to have.
Well, the wording is rather clear that it was about English.
Note that the author stealthily added a precision to his comment (which originally ended at "why regress?") since then to make clear it was about having a common language. But he has not removed the offending part.
Adopting another language as our lingua franca when English is already filling that role would be a regression. It's not saying other languages are inferior per se, they might be superior. But using any other would be an inferior choice now. It doesn't mean we can't add local flavors to it.
I am a French native speaker and I also think we should just use English and move on as a species. Interpersonnal communication is hard enough that we don't need artificial complications. Let's tackle more interesting problems. Same reason we should use a single measurement units system, mains current standard, a single currency, etc.
It's extremely offensive to suggest that English is progress and other languages are a 'regression'.