I don't agree there. Explanation would be more "I do/think/believe X because" where indoctrination is more "you should do/think/believe X because".

A more passive form of indoctrination would be repeated explanation (with or without query/prompt) so explanation can become indoctrination depending on context, but I'll stand by my choice of words above.

Your examples answer the wrong question.

"Where do rainbows come from" can be answered with the explanation "As a way to show God's promise to Noah never to flood the Earth again" or with the explanation "because sunlight refracts through water into all the different colors we can see" or with the explanation "invisible unicorns fly through the sky sometimes and leave rainbows where they've gone".

Many people would call one or more of these indoctrinations, despite the complete lack of "should" in any of the responses. Egocentrism does not a benignity make.