Well they are the Roman/Greek names for them, so they are going to probably be a bit off. Mind you, the real, original names the tribes themselves used were probably much worse! Given that they probably spoke something close to Welsh.
Whenever I see the Iceni, for some reason I always think they are the forefathers of the modern food chain 'Iceland'. Don't ask me why.
Mind you, what are the 'Belgians' doing around about Bristol??
I was going to go all pedantic @Phyrebratm that these are Iron-age tribes, not stone age ones, but RuralHistoria gets it right!