Would it work in this case? Had he asked about this in a team, he would be told about the existing approach and that'd be it. I've been on the both sides, as junior questioning common practices and as senior answering such questions - and it always resulted in transfer of common knowledge, not some breakthrough.

I totally support searching for the new truths, but we must not forget why the phrase "do not roll your own crypto" exists. It is ok, or maybe it even MUST be done by students and researchers, but I am not so sure about juniors working on production systems. Still fine if you work in R&D department