This is reasonably true. But there is also some likelihood that the hospitality and guest-right system was not only very old (since it is found across many other Indo-European branches as well) and part of this. Isn't there an episode in one of Homer's poems or something (I don't have my library with me in Indonesia :-( ) where two people are fighting on the battlefield and discover that one of their ancestors gave hospitality to the ancestor of the other and so they have to quit fighting?
Oh yes. Hospitality is the central theme of Genesis 19, for instance, which definitely predates The Wanderer. I feel a little bad now, because I can't provide you with a solid set of sources, but every culture all the way back to the earliest stories we have will give references to the obligation of a host, the duties of a guest, and how gift-giving plays into that. The whole point of the Trojan War wasn't precisely that property had been stolen, but more importantly that it had been done by a guest to his host. (As modern readers, we recognize a breach of private property more clearly than we recognize a breach of hospitality.)
It's the earliest form of debt-as-community-glue, really. It only survives today in the habit of bringing a bottle of wine to a dinner party, and in the handshake. We mostly rely on codified laws of hospitality instead (which govern restaurants and hotels).
Back then, these things were evidence that the other guy wasn't going to knife you in your sleep.