Unfortunately it is impossible (or nearly impossible) to measure the "majority" in bitcoinland. There is simply too diverse of a population of stakeholders to possibly be able to accurately be able to poll all of them, in addition to the fact that the various stakeholders of Bitcoin may have competing interests and may not be in line with the best interests of Bitcoin. Some stakeholders may not even own nor use Bitcoin currently.

I would personally opine that major economic companies (collectively, not individually) should be the ones who decide if a HF (or features for a potential HF) should be adopted, as they ultimately are the ones who give bitcoin it's value and they are the ones who can best measure the opinions of Bitcoin users (as if several large of their customers are in favor of, or opposed to a certain proposal they would know, and they would be able to easily filter out sockpuppet type opinions because they can easily measure by transaction volume). I would also say that the opinions of the miners should be given fairly strong weight due to the fact that (as of now) they have invested heavily in what is essentially the success of Bitcoin and their best interests are generally going to be in line with that of Bitcoin.

I would say that it looks like that they figured out that Blockstream et al. doesn't have any intention of actually delivering a HF that increases the maximum block size, and they want to be sure that they will not get tricked into giving Blockstream et al. what they wanted and not get what they bargained for in the end.