I think you're probably right, but... Twitter's implenmentation of authentic user detection must be expected to try to separate normal users from e.g. test acc

I think you're probably right, but... Twitter's implenmentation of authentic user detection must be expected to try to separate normal users from e.g. test accounts created by client authors. And even if the Media Matters staff was genuinely interested in seeing etc, I think it's quite likely that their click pattern resembled a test account more than a Joe Normal User. (Intense activity immediately after signup, for example.) If that's the case, then Twitter's authentic user detection would classify the MM user as "likely test account" or something like that, and the authentic user data shown on Twitter's dashboards would exclude the MM user.