I would set up a workflow that uses the Data Value Changes step and identify the field in question.
And/or make sure that the smart list says
Fills Out Form
Field X IS NOT EMPTY
1 of 1 people found this helpful
Instead of the fills out form trigger, you should use a Data Value Changes trigger, Attribute: <your field>, Source Type: Web Form Fillout. This will make the campaign only trigger as a result of a change via form fill.