It seems like a semi-regular thing. I'll try and check to see if they're on 6300 kHz USB again this afternoon/evening with the strange language. I could certainly hear Spanish in the background but that was another QSO (at first it seemed like the Spanish-speaking op was trying to talk to the stronger station, but he could have been working the other Spanish speaking OM on frequency, it was pretty messy for a bit).
Considering the amount of traffic coming out of the Caribbean and Latin American areas lately it wouldn't surprise me if we were listening to some sort of Afro-Caribbean marine net, similar traffic has been heard all over the 6-10 MHz region.
Looks like others have heard this UNID language, not sure if its the same group but here's a log from 2016:
https://www.hfunderground.com/board/index.php?topic=27683.0