I think by immigrant communities he was also including immigrants children (1st 2nd generation or more). I've seen this used as to visible minorities in many places around the world. Including country that are mostly immigrants like Canada (where I'm from).

What has been reported is that it's youth from poor neighborhoods. Considering the population composition of those neighborhoods, I'm going to guess that it's probable the groups are composed of a majority of people from those immigrant communities. It still doesn't mean it's a immigrant riot. I bet poor non-immigrant (as in their family always been there) are also participating.