I believe, if you know the required BTU of the heater, the gas service pressure, and the gas line diameter and length, you can calculate if you're theoretically getting enough gas. That is a question for a heating pro though. I just thought you would like to know so you can arm yourself with questions for the next service visit.
More likely it's spider webs in the tube that tells the controller than you have enough airflow so that it will then open the gas valve and start the igniter. The home warranty company tech probably read the troubleshooting guide and figures low flow must mean the gas.