I'd ask if you did the logical thing and reached out to BMC (you know, seeing it's their bike and label) but I'm going to assume you haven't and made a post here, instead.

We had a batch of Pinarellos at the shop that also had similar stickers. In looking at all of our 2017 BMCs in the shop (moments ago) they too have the "don't use on the stationary trainer" sticker.

I'm waiting to hear back from the BMC rep, just dropped him an email, but considering how many BMCs I've seen in trainers (and how many I've ridden in trainers) I see absolutely no reason why you can't use a trainer with a BMC. I suspect, much like other warning labels, it's to cover their ass in the event you put your expensive bike in a trainer, don't properly secure it and then try to blame BMC for shotty workmanship.

Around this time of year we see an uptick in people who don't properly secure their bike to a trainer, cause a problem (or worse, damage) and then try to peg it on the frame manufacturer.