I can't follow any logic underpinning the "proof" so positively claimed as the "only motivation" in that conclusion?
I suspect that their genuinely held concerns are environmental, though not necessarily thought through.
Here more, it is just an easy target for expressing their view, and provoking a reaction.
I believe there is unlikely to be a hint of jealousy, let alone it being the "only motivation", in owing something that they don't need, want and see as unduly polluting; why would there be?
An SUV pollutes more if it is older technology, and only reflects the amount of use it sees; parked up it pollutes less than the protester does.
In some cases they are probably right in the belief that the ownership and use of a SUV, and with it the "extra" pollution is unnecessary in being predominantly a vanity choice, better handled by something less polluting.