I would start getting my oil changed somewhere else if the guy is running your engine while pouring oil in. Like Larry said there is no vacuum, oil is pressured through the filter. You should be fine if you drove and your oil was at the min. level. This thing to learn from this is to check your oil more frequently, like everytime you fill up, or every Saturday morning. Also, long hard trips can burn condensation and contaminents from your oil and that will lower your level. So check it after long trips or hard driving where the engine was hotter than usual. I always keep a full gallon of oil in the trunk in case I ever need it. 7 bucks is cheap insurance.