Programming question of mission planner

Hello. Please be generous because I’m new to programming.

I’m recently dig into mission planner plugin programming. it is very interesting.

I have experience on VBA, which is similar to CSharp. in the VBA, message box or input box was modal, and calling it stopped UI thread.

but I found that calling this input box doesn’t stop the program loop.(as you can see in the attached photo)

I can’t figure out how this is possible.