To add to what nehanarkhede said: I'd rather see it as a testament to the powerful building blocks of Kafka and its Streams API that you can actually implement a project such as KSQL with very few engineers.

Also, the commits in KSQL reflect only parts of the work -- it doesn't include design discussions, code reviews, etc.

Lastly, keep in mind that the git repository was cleaned (think: squashed commits) prior to publication, see the very first commit in the repository's timeline. So you don't see the prior work/commits of other Confluent engineers that went into KSQL.