While it may be true that some place-names in Iran reflect the presence of the Kassites, the ethno-linguistic origins of the Kassites isn't clear at all. There may be some agreement that they may have had contact with Indo-European groups, which may be reflected in some proper names, but the majority of the evidence of language seems to point to a Hurrian or Hurrian-parallel background. The following are a sampling of Kassite words or word-elements which have their equivalents in Hurrian words:
KASSITE HURRIAN MEANING
ab- abi first
ag- ag- to lead
al-, alb- al- 1. to bring near to 2. to speak
amm- amm- to reach, come close to
ar- ar- to give
asht- asti woman
at- attai father
ba- pa-, ba- to build
badar pedari- bull
bur- buru strong
buri-, ubri- evri, erbi lord
dan- tan- to do
dup- tuppi strong
durug- turuhi male, man
en- an- to rejoice
etc............
Yeah, no two scholars agree on their origins: one thinks Hurrian, another thinks, Elamite, while a third thinks IE.