Paul was not here referring to just any type of prisoner. He was speaking about those brothers who were imprisoned for their faith.
لَمْ يَقْصِدْ بُولُسُ هُنَا ٱلسُّجَنَاءَ عَامَّةً ،‏ بَلِ ٱلْإِخْوَةَ ٱلَّذِينَ يُحْبَسُونَ بِسَبَبِ إِيمَانِهِمْ .‏