The rich stay rich, more than the poor stay poor (in Canada).
But the number is about [relative change in income across] the population - if most people are poor (which they are) high mobility across the population likely means poor people are moving up (or indeed getting much poorer - halving your income when you're already in the lower quartile would probably be as big a shift as doubling it - if not more).
http://www.statcan.gc.ca/pub/11-626-x/11-626-x2016059-eng.ht...
The rich stay rich, more than the poor stay poor (in Canada).
But the number is about [relative change in income across] the population - if most people are poor (which they are) high mobility across the population likely means poor people are moving up (or indeed getting much poorer - halving your income when you're already in the lower quartile would probably be as big a shift as doubling it - if not more).
You're right to ask for more detail, though.