The Kingdom of Bosnia with its own identity and cultural heritage was a thing though. I would recommend you to check out the following sources:
An introductory read:
For further info on the region during the Middle Ages I highly recommend following books, which synthesize Serbocroatian sources from all regions, mentioning controversies from different strands of scholarship:
Calling the inhabitants of the Banate of Bosnia resp. later Kingdom of Bosnia Serbians is simply incorrect, especially when looking at the fact that Bosnia at this point in time was quite isolated from both the Catholic Church and the Eastern Roman Empire at this time. Probably due to the weak implementations of both churches in this mountainous region, Islam was adopted fast.
You can find both books on the Internet archive: