@gennoson : Unforunatly this site is filled with to many idiots trying the prove their mental superiority.
For theeecord I knew you were talking about Greek Fire (a famous ancient super weapon, if you have any knowledge of things beyound like 2 centuries ago you have almost certainly heard of it, but it is not the only famous list tech. Damascus steel is another, the modern version is not the same. so much has been lost to time it is not funny.
Plus development in one area does not mean you are developed in all areas, so a less advanced in general society could be more developed in 1 area with little issue. Like how the most successful arctic explorers were the ones who learned from the Inuit and other natives, they were less developed in almost every way, but much more capable in terms of dealing with the cold and arctic survival. A lot of development comes from necessity and accident, if his world did not need dimensional magic, then it kight never have happened.
Of course the more likely issue is probably closer to sliders, hopping worlds is possible, but targeting the right one when he was not prepared for the summon might be exceptionally difficult, and random travel is effectively suicidal.