Critical Role was a home game in 3E/4E era. It became a show in March 2015, by which point all 5E rulebooks were released.Vin Diesel, Steven Colbert and several others were talking & sharing their experiences before 5E came out. Critical Role started back in 3E/4E. Sarah Connor Chronicles at one point had the terminator playing D&D. Before 5E came out, it was already on an uptick. It just seemed that with 5E's release it really started to come on strong as the latest version apparently was more approachable to returning gamers.
Stranger Things was not the end-all-be-all for 5E's success, and 5E was immensely succesful right from the get-go in its niche hobby audience. But things like Google Trends data clearly show that D&D reached mainstream popularity following Stranger Things's release.