Is that strange because they aren't Brazilian?

They are Brazilians with paulistas accent. It's strange that they are, all, Brazilians.

As a Brazilian it makes sense to me, Brazil economy just keeps getting worse and worse, a lot of Brazilians are moving abroad chasing some opportunities. London is very famous as a destination for them, before there was Deliveroo I knew some people who did a lot of construction work because a lot of firms would hire them even if they don't have the proper visa, I assume you can do the same with Deliveroo.

A lot of Brazilians (allegedly) come in on fake Portugese documents too

I always assumed most people just come in pretending to go with short stay tourist purposes and try to stay under the radar while living there. London is so expensive anyway most will probably be squatting.