This is a bit longer, you may well disagree, happy to hear your (alternate) perspectives!
TL;DR: There is various historical reasons and parallels why “Revolution” can be seen as an apt
description of the OS R.
Below is my rationale and reasons why for myself personally at least. “Revolution” is the most apt (as much as I like the descriptors “Revival” and especially “Renaissance” as well!):
A. When D&D first appeared it was truly revolutionary, a quite big departure/off-shoot from wargaming and absolutely unlike any other game on the market back then. D&D spawned an entirely new vocabulary, way of gaming, hobby and industry. It had and still has profound influence on (sub)culture, (RPG) computer games and more.
Since D&D 5e and adjacent phenomena like OSR became very popular (currently we are in the Golden Age) some years ago, there is a continuation or re-ignition of the original revolution, the 1000s of OSR Blogs, exploding amount of players not playing (only) vanilla D&D/HASBRO, many 1000s of OSR products and many dozens of streams and Youtube channels featuring OSR topics and sessions are examples of that.
B. When I personally first discovered OSR, it led to a true revolution in my own RPG thinking, rules, inspiration, manner of play, creativity and involvement with the hobby despite having DMed regular D&D for more than 2 decades at that point. Very few other concepts or things I encountered in life had this much and persistent effect (Open Source software or Punk/DIY culture would be 2 and I do not think that is a coincidence, they share quite some -revolutionary- aspects with OSR). Discovering and implementing OSR concepts, rules and thinking made my games better, faster, more inspired, more realistic and above all more fun!
C. It is a revolution of sorts in that small (often one person) operations, writers, game designers and publishers compete for attention (and to a lesser degree purchases and dollars) with HASBRO (WOTC),… which is a massive moloch of a company that owns scads of IPs and has a net worth (as of December 17, 2021) of $13.64 Billion,… Plenty of OSR (adjecent) type publishers only sell 100s or 1000s of copies, but there is also outliers, such as MOTHERSHIP which recently picked up more than $1,400,000 in a matter of weeks on Kickstarter. HASBRO/D&D is not going anywhere, and that is not a bad thing, but simply having OSR around makes them have to up their own game, and having a choice or being able to enjoy both is a real blessing for any consumers or players.
Because the best exponents of OSR are so varied, active, passionate and especially creative, OSR type products tend to win 50% to 100% of all the Ennies in the last years. That does remind me of a smaller but very committed revolutionary force taking out -or at least taking a big piece out of- a monolithic powerplayer. The fact that the OSR influenced and changed (1 or 2 people prominent in OSR scene were hired as consultants for 5e and the authors of 5th have stated they looked to OSR blogs for plenty of inspiration some of which ended up changing how 5e was written/in the rules to at least some degree is more evidence that OSR thinking/way of doing things is not all that niche in the final analysis.
D. It is fairly revolutionary that plenty of OSR products are free (or pay what you want) for PDFs, Open Source and/or Sold at -very low- cost for a print copy (Basic Fantasy RPG). This started with the Open Gaming License and Retroclones but has had additional far reaching implications and effects. This free and libre exchange of ideas, rules, concepts and the forking or building on top of existing OSR offerings of all kinds, harnessing self publishing and print on demand, all that means that permutations and evolution (while still also looking and going back to proven editions or rules) are near endless.
If, in your case OSR was somewhat revolutionary, in what ways and to what degree? Would love to hear your thoughts and experiences! 
If not at all, also happy to hear those thoughts.