Yep, that's what I heard too, from friends and colleagues working there.
We had a bunch of PowerMac G5's at Framestore back around 2004-2006 in the Texture and DMP department. They were fantastic to work on but were phased out around 2008-2009 because they didn't want to spend the extra money on specially trained Mac IT support staff. It's all PC workstations now running Windows and Linux.
At Weta Digital only the production/coordinators had Macs, as well as some sort of proprietary software running on Macs for their dailies sessions. But most VFX sups complained about it due to the frequent occurrences of the dreaded spinning rainbow during client sessions. (I can tell you, James Cameron is not a patient and compassionate man, haha ) I think their art-department had some Macs, but certainly not the 3D teams. In fact, the IT department laughed at me when I requested a Mac. This was around the Avatar period, not sure what they've got now. I'm guessing mostly PC hardware.
MPC London (don't know about the other sites) never used any Macs for their 2D and 3D artists. Only MacBooks for their producers/coordinators. Simple stuff only.
Now I'm here at Square Enix Tokyo and not a single Mac in sight. Have yet to even see one since I started here a little over a year ago.
So yeah, it's safe to say that Apple blew it with the VFX and game industry. There was a significant upsurge in interest from said industries when Apple went Intel and it looked good for a few years. But they've since turned their backs on us. Even if Apple somehow manages to come out with an incredible new Mac Pro, priced very competitively, it will take a looooong time and a lot of subsequent upgrades/products accompanied by pro-level support and macOS upgrades to win back the trust of the 3D community.
And don't forget that time they bought then killed Shake.
Of course I think that was kind of a forgone conclusion given how bad the codebase was. When they killed it they offered us the chance to buy the source code. We did and apparently it was a complete mess.
Still didn't endear Apple to the VFX community though (even beyond them abandoning the pro time and time again).
And now they are dropping openGL in favor of metal. Another step in the wrong direction if they are interested in the high end 3D market (note: they aren't actually interested. We are simply too tiny as a market to make it worthwhile).