I feel like there is a large room for error here:

* how many people who are watching a stream have some sort of adblock enabled?

* ads on twitch are not deterministic: some people (even without adblock) wont see ads

* how often do these streamers really play ads?

I assume that twitch (or at least the advertising partner) can tell that there wasnt a request to pull the ad (in the case of adblock), and so no ad was shown and thus not compensate the streamer. But given this possibility, the numbers could be off by a large margin especially because ads seem to be the primary source of income for these streamers.