Can high iron levels be caused by dehydration?

Depends on details: Dehydration has different meanings depending on one's perspective. Many non-dehydrated people say they are dehydrated, because equate being extra thirsty with being dehydrated. Iron levels are just numbers, several of them. They have little meaning unless a doctor sees the whole picture. That means there is no good answer here, without knowing many details of the case.

Details matter: "High iron levels" needs to be defined. "Dehydration" needs to be defined. Hemochromatosis is serious. Ask the Dr who ordered the test.