Interesting. This could be a bracketing error, because I read
> it includes analysis of many older accounts that haven’t sent tweets in the last 90 days and thus, likely don’t fit
> Twitter’s definition of mDAUs (monetizable Daily Active Users)
As implying that they think accounts that haven't tweeted in the past 90 days don't fit Twitter's mDAU definition. Given the placement of the qualifying phrase, I think that's a reasonable parsing of the sentence, but I see your point that they could be trying to imply their set doesn't fit the definition. If so, that sentence is very badly constructed.
> it includes analysis of many older accounts that haven’t sent tweets in the last 90 days and thus, likely don’t fit
> Twitter’s definition of mDAUs (monetizable Daily Active Users)
As implying that they think accounts that haven't tweeted in the past 90 days don't fit Twitter's mDAU definition. Given the placement of the qualifying phrase, I think that's a reasonable parsing of the sentence, but I see your point that they could be trying to imply their set doesn't fit the definition. If so, that sentence is very badly constructed.