Observation as a substitute

Is it common to have someone pop in for "observation" as a substitute?

Long story short.

One of my very first sub gigs I had someone pop in for "observation".

I went through the normal CKH routine of good things etc.

Then went into classroom lesson plans.

I overheard the observer say "I've seen all I need to see".

And that was the end of it.

I never saw or heard back from that person again.

But shortly after I was quickly snatched up by district and hired as a Paraprofessional.

Is it common to get "evaluated" I guess that what observation means. As a sub?