The Mapuche word traf means “wall”, but metaphysically it is also connected to the idea of “facing” or “meeting”, e.g. the compound word trafün means a “meeting”, connected to this idea of facing something and meeting it, connecting to it. This word is thus not the best example of showing a similarity with the Finnish word kivi - “stone”, however, when we consider the deeper metaphysical meaning of “connection” and “faces” implied in the word traf, it could also be argued that a stone, kivi is also “faced” and is also a material which is connected, bound, on a molecular level. Note also that traf is pronounced [tsaf] making it quite close to the Finnish word kivi. Note also that many other similar words for “stone” are present in other indigenous languages of South America, which I have discussed elsewhere, one example being Arawak sībo - “stone”. 
Mapuche also has a large number of similarities to Indo-European languages, some examples I noticed recently are zungun - “music”, compare English “song”, Dutch zang, Swedish sång etc. One of my favourite examples which I have mentioned in other publications too, is Mapuche dungun - “language”, compare English “tongue”, Icelandic tunga, etc. I have mentioned many more in other publications.