@George,
You make a point worth considering, George. Of course, in the instances you describe the process took years if not decades, and instead of three random individuals taught by sailors, there was chance for natural linguists to emerge and in some cases for a more structured learning process.
When I see how badly English sailors maul French or Spanish or Italian place names and words, never mind acquiring a working knowledge of the language, the idea of Spanish sailors doing this for Quechan or other native tongues strikes me as preposterous, especially in the time frame proposed.
In my experience individuals may learn a word or two by pointing at objects (which they usually mispronounce and promptly forget), but to communicate something like learning sociopolitical relations and proposing a military alliance against common enemies, etc., strikes me as improbable under the circumstances.