Tourists are highly likely to have money in their pockets and expensive gadgets with them, so they tend to be easy targets.

Someone foreign who learns the "ways" of the locals would easily be able to mingle though and go mostly unnoticed (Brazil has had peoples of all races for a long time, it's not like you stand out much by being blonde or asian, for example). And any local will immediately tell you to never walk around with money or expensive devices, and specially, never flash them around no matter where you go (near favelas there's a lot of unemployed/poor/desperate people - no one wants to live in one... so it ends up being a lot more dangerous in general than anywhere else).