I really appreciate this analysis. When I first heard the "20 new people move to Durham a day" quotation, it was from a mayoral candidate who is now Mayor of Durham. I too wondered where that number came from and thought it was a Chamber of Commerce statistic, or from the City of Durham. Further, there is a very intense narrative around how long-time residents in East Durham are getting pushed out specifically by new residents but if the net migration is actually negative, then that implies something different.
I'm not sure these numbers are inconsistent with the East Durham gentrification narrative. One of the consistent issues seems to be that people are tearing down houses and building new ones, and that the new residents are disproportionately white Millennials (like me) who are replacing lower-income, mostly black residents. If these are singles or couples replacing families (on average) then the net migration could certainly be negative.
Another caveat, the newer houses tend to be bigger, and it's possible that the number of housing units is actually going down in certain places as smaller numbers of big houses replace smaller houses or duplexes (though the total square footage may be similar or going up, as housing stocks change). I'm obviously just speculating, but this seems plausible to me.