While some of the comms could be legit, considering the band involved, the bulk of the comms likely are HF satcom pirates.
Brazil is on a good location to access open transponders on the US military FLTSATCOM 8, and its transponder relay signals often can be received from South America to North America. Pirates range from casual comms in Portuguese, to playing music, and whatever else.
There have been crack downs on the activity in the past, but the need for international coordination to do so means few of the SATCOM pirates seem intimidated.