RED+BLUE=BROWN?? - RED is NOT a primary colour?

Art Materials used in this video:

Schmincke Horadam 24 pan set:
Amazon USA: https://amzn.to/4g0JEl1
Amazon UK: https://amzn.to/4gk85ub
Amazon DE: https://amzn.to/4fFmW2g
Amazon NL: https://amzn.to/3V6ybZr

Cotman Watercolour Brush size 8:
Amazon USA: https://amzn.to/3ZkBjDr
Amazon UK: https://amzn.to/4eJwTKD
Amazon DE: https://amzn.to/3Z6gjia
Amazon NL: https://amzn.to/3Z3ovA3