That's not what the article says.
The article says that an extra 50,000 pensioners will be put into relative poverty which is defined as having less than 60% of the median income.
Was going to make the same point.
People can drop into, or move out of, relative poverty on the basis of changes in national median income even if their financial position doesn't change one iota.
But there are further reasons why relative poverty is particularly unhelpful for people over 65 as it is calculated on 60% of total median income and doesn't take account of housing costs which are typically way, way less for the over 65s than younger groups. I've seen some recent data which shows that when housing costs are removed, then over 65s are the least likely age group to be in relative poverty.
But there are more factors - specifically deductions. Most age groups need to pay NI at source, while those over 65 don't so their effective tax rate is lower. Add to that that many of the younger age groups are now having further deductions at source for student loans and that's before you might add in costs of supporting children etc.
So matched income for income, over 65s will have much higher disposable income than other age groups and I would suspect that an over 65 person at the relative poverty threshold (the people that this article focusses on) is probably as wealthy (if not more) in terms of disposable income compared to someone in a younger age group on national median income.
That isn't to say that there aren't pensioners in genuine absolute poverty, but that using relative poverty is a particularly bad metric in this case.