Not to defend the shitshow racist posturing of deporting people without legal advice who are the UK's responsibility, but that isn't the best argument by Rosen.
Jamaicans are spectacularly overrepresented in prison. I just found the figures for 31 December 2018, couldn't see more recent ones.
Total for Australia, Canada and New Zealand 32
Lots of the Jamaicans will be drug importers. We can certainly argue about those drug laws (and the role of race in how society sees drugs) but while they exist it's not surprising that lots of Jamaican nationals get sent to jail for longer than 12 months and deported afterwards.