Plates

Question

Someone who thinks he knows halakhah told me that you can't have them put your kosher meal on one of the caterer's plates because one may not place hot food on a non-kosher utensil, even if it has not been used fo rhte day, and only if this was already done is the food permitted. Please explain why he is wrong (we got into an argument at the affair and now he thinks I am not very kosher) Also, please explain what the difference is when it comes to your own plates and someone else's plates (e. g., we don't put hot meat food on a dairy plate)..