They mentioned gold with this question, with answer like: "You buy piece of rare metal that's durable, rare and shiny"

While technically correct, this answer doesn't touch the 'store of value' or 'distributed value ledger represented by pieces of it" aspects of gold. And as such this answer is not an informative answer. Answering this question with gold have similar issues as bitcoin. It's just a coincidence that gold have physical representation that can serve as a basis for this technically-correct-but-not-so-useful pseudo-answer.

If you really are satisfied with "piece of metal" answer for gold, I guess you could create similar answer for bitcoin: "You buy a rare, durable metal with atomic number 0, which means it doesn't have any mass and exists only as pure information".