depending on if you just call all rock from japan jrock, or if jrock is a certain type of japanese rock and pop groups...
It used to be used in the first sense, and as far as I can tell was never used in the second sense until JRR started using the word "Jrock" to promote a roster of exclusively visual kei bands.
OK, here I go with one of those annoying "back in the day" stories, Storytime with Uncle Hollywood again.
Back in 1996 when dinosaurs walked teh internets, I discovered my first Japanese rock band (Luna Sea), went online to get more info about them, and from there went on to find X and B'z and whoever else. Back then:
1. Jpop was by far the most popular form of Japanese music online. You had to wade through the pop sites (SMAP, V6, MAX, Namie Amuro, whatever) to get to the rock.
2. Everything that was "harder" than boy bands was usually called Jrock. Basically, bands where they play rock instruments rather than sing and dance. The pop-rock bands, like Glay, L'Arc, and (at the time) B'z were alternately called Jpop or Jrock. Let me make this really clear,
ANY rock from Japan was called Jrock at the time.
3. "Normal" Jrock was normal. The non-visual or used-to-be-visual-but-not-anymore were WAY more popular than the visual bands. Visual kei, which at the time was called "visual rock" or "visual shock", was a niche genre for freaks and enthusiasts. (Much like it is and always has been in Japan.)
4. Other than Luna Sea, X Japan, Kuroyume, and Penicillin, visual rock was fucking hard to find information about, let alone actually buy. What few online stores there were, private sellers included, sold only Jpop and non-visual Jrock. If you wanted visual, you either had to know someone in Japan, or else you had to use a very mysterious and arcane fax process to order from Third Stage, who did not have a web site at the time. If you actually succeeded in ordering something from Third Stage, you were the coolest person ever, or at least the coolest person that week on inertia's visual BBS.
Over the years the visual stuff gradually gained popularity. Skip ahead about 10 years, and all of a sudden Jrock Revolution appears and declares themselves the be-all-end-all of all things visual and "Jrock". They create a surge of new visual kei fans, who naturally take everything JRR says as truth. It's not the fans' fault really, after all, JRR presents themselves as the ultimate authority and the new fans don't know any better than to simply accept that. I wouldn't be surprised if many of JRR's employees are in fact themselves too "young" in the scene to understand its history, and the older fans who have been around longer unfortunately seem to see no need to correct any of their misconceptions.
Jrock 101 is pretty scary since a lot of what they present is poorly researched, leaves out some important points, or is simply wrong. To use a very trivial example that still illustrates the problem pretty well, I remember a Jrock 101 topic about why no Japanese rock musicians ever have green hair. The very existence of that topic amused me, but anyway, it's simply incorrect-- INA, the guy in By-Sexual, the guy in Color, etc., all had green hair. There was another topic about how Japanese rock musicians never do drugs and never die of overdose, or something like that, which left out Hisashi Imai's LSD arrest and Kazuki's (Raphael) fatal overdose on sedatives.
Anyway, what this all comes back to is that JRR, a source of much misinformation and little historical perspective, is almost certainly where this notion of "not all Japanese rock is Jrock" originated. Because they call themselves "Jrock" but all the bands they promote are visual. And understandably from a marketing perspective, they seem to let this misconception flourish, probably because it benefits their brand if people associate the currently-popular visual stuff with the word "Jrock" in the name of their company.