Email campaign source confusion

Your software
My Mautic version is:2.6
My PHP version is:7.2

Your problem
My problem is: in campaign builder you can select source as the signup form or the segment.
So I chose email form and then connected that one to send email to user when they fill up the form and also automatically add user to segment.
But what if I import 1000 users into segment they will not get inserted into campaign right?
WHat is the proper way to do it. To create new campaign just for segment source? Or use both form submit and segment source in 1 campaign?

These errors are showing in the log:

Steps I have tried to fix the problem: