I think the connection is completely possible. The origin of the African slaves can be traced back to regions by their DNA, but the project is still work in progress. I think the Wasolon region is not as far from the coast as to have made enslavement of their people impossible. Also, you don't need large groups of people for their musical heritage to thrive in a community. Among the African slaves in Peru, craftsmen like smiths had a privileged position in society, they held the highest social status and thus income and liberties to live their inherited culture. From smiths to djembe-music is not a far cry.
I just listened to Festejo music and I think its origin in West Africa cannot be doubted. Isn't it clear in Peru that this is the music from Afro-peruvians? At least these are the typical hits you get from a search on youtube of groups doing this music in Peru.
But why do you think specifically about N'gri, Cote? There are many rhythms with such a bell-line in West Africa. What other indicators do you have? I would be interested in some details.
To find out more about the cultural background of N'gri I would directly get in contat with Rainer Polak:https://www.rainerpolak.de/
He can certainly tell you more and perhaps knows where to search for even more details.