They didn't send an engineer from Detroit to come look at your truck. What they sent was a FSE, Field Service Engineer, that is located in all of the sales districts to help troubleshoot some tough problems. These guys have access to all the goofy repairs for problems all across the country, so they search the database for problems related to an evap code (I'll bet this is a F150 problem and not just an ecoboost issue) and see a trend where they have found a foreign object in the evap hoses. So once he goes through some of the basics with the tech to make sure the guy knows what he is talking about, he/she had a pretty good idea what to look for. Unfortunately Ford isn't really good at sharing info like this with us techs.