Those trends may appear correct today, but he’s forecasting out 40 years and no one knows what will happen over two generations. Those projections are based on what we know about the future, which is ... not much.
Maybe Euro-Americans will begin procreating beyond bare replacement levels again. Maybe some will migrate back to the Middle East or Asia, South or Central America. No one really knows how the world will be in 40 days much less years.
I remember some tv anchorette swooning back in ‘81 about how the then-19 year old Diana will one day be Queen of England. So much for that.
Demographic forecasting in the US has generally been accurate and the only errors have been an underestimation of population growth and more specifically the underestimation of the expansion of current minority groups.
Texas for example in now a “minority-majority” state meaning that blacks and Hispanics combined make up greater than 50% of the population. And while that fact has had little political impact this far, it is likely to have a great political impact in the next ten years when Texas becomes a Democratic state.
At that point in time, the Electoral College math gets very difficult for the GOP when going into a presidential election, they have to spot the Democrats; California, Texas, New York, Illinois and Florida before the first vote is cast.
That’s 168 Electoral College Votes for the Democrats before you begin to add in the other Blue States.