I suppose “poor” is a relative term, and as you say, since we’ll all be poor, as I totally concur, so in essence, no one will be poor.
The problem is that the author of the article used the term 'poor'. If you actually read the article, Gates uses the phrase 'extreme poverty'
Living on $10/day is poor. Living on $1/day is extreme poverty
Gates is actually right. Most of the world is above extreme poverty and probably, tho not certainly, those residuals in Asia and Africa will rise out of extreme poverty in the next few decades.
So Gates wants to dispel the myths and these myths arise because those who live on a $1000/day, $100/day, or $75/day look down on those at the lowest incomes of $1/day and $10/day, $20/day and can't differentiate between them.
But the guy living on a $1/day can easily see how much better off he would be at $10/day, or $20/day, or $100/day.