Actually, this is mentioned in the article, in the "HOW MUCH DO DIFFERENT ROCKETS EMIT?" section, and gets more into it in the linked raptor article[1]
> Although all rocket engines do run fuel rich for the right balance of heat management and performance, so there is likely going to be unburnt fuel expelled regardless of the cycle type, but much more when it is an open cycle engine.
> Although all rocket engines do run fuel rich for the right balance of heat management and performance, so there is likely going to be unburnt fuel expelled regardless of the cycle type, but much more when it is an open cycle engine.
1: https://everydayastronaut.com/raptor-engine/