That's the most oddly worded "rule" i've ever seen. Sounds more like a guideline/warning
"Rides are suitable for conventional & electric mountain bikes, hardtail or full suspension only"
....so if you turn up on something stupid you might break it, fall off or get left behind.......
Unless you know what you're doing. TBH, the last MTB club ride i did, 99% of it i could have got round quicker than most of the riders on my CX bike, the 1% i'd probably have run (and only been a little slower.....)
Oooo I don't know about that Peachy, last time out in Dalby was on the Fatbike( between lockdowns), I has some E-bike full suss weekend warriors up my backside for a few sections, they were whinging and moaning at being stuck behind me on the ups but funny thing was they couldn't keep up with me on the downs