The person you saw was probably an old neighbour of mine. It didn’t matter what you cooked; he wouldn’t even taste it and would always start pouring that ketchup bottle over everything; on the odd occasion, he’d use Maggi.
Tomato ketchup is simply a sauce made from tomatoes and then cooled. Sugar may be added, but this isn’t necessary. The sugar is often added to counteract the acidity of the tomatoes or to make it keep for longer.