During screen sharing in meeting, someone was able to draw a (curved, red) line

My issue:

During screen sharing in meeting, someone was able to draw a (curved red) line *onto* the shared screen.

It was not the (guest) person that shared, it was not the host (= me), but some meeting guest.

My questions:

Any idea, how this is possible, please?

Can host prevent this?

Thank you for any answer/solution and/or idea!