I've just had a similar conversation with my Japanese wife, and she pointed out that with many of the words that can be interpreted as nouns or verbs by fluent

I've just had a similar conversation with my Japanese wife, and she pointed out that with many of the words that can be interpreted as nouns or verbs by fluent speakers, she only knows one interpretation, so she misses the 'garden' path that a fluent speaker would take. I suspect that it also applies to transitive vs. intransitive verbs. So to contrive your example, a fluent speaker would know both the transitive and intransitive uses of "returned" and, preferring the intransitive interpretation ("I returned home"), would reach your conclusion. But if a non-fluent speaker only knew -- or was stronger with -- the transitive version ("I returned the book"), they would arrive at the correct interpretation. I hope that makes sense, it was a lot harder to explain than I anticipated!