It sounds unlikely. I believe it has the same very light frame as the 905e, and as the photo below of over 6' Wisper director Doug on a 905e below shows, 14 stone doesn't appear to be a limit:
That's the same bike, but maybe the 90 kilos isn't related to frame strength but something else like braking. I'm minded of Shimano's 100 kilo rating for their hub roller brake, which on the e-bikes where it's often fitted is frequently exceeded.
This is worth checking with David Miall of Wisperbike, since he is the joint owner of the company, here and in China, as it's a serious restriction.
Hi Mabsey, Doug here from Wisper, I am 18 1/2 stone and ride 11 miles every day, sometimes even more when I take it on the tracks in the forest but my arms ache after that! regards doug