This article seems like empty semantics to me. As they say, "not your keys, not your coins": controlling the private key feels like a reasonable proxy of "ownership" in common parlance.

If you want to get really pedantic about it, then contrary to this article's assertion that

> Bitcoin is “stored” on a the public blockchain

The blockchain is just a record of transactions showing the movement of bitcoin values between wallet addresses. It's not like "a bitcoin" is some discrete thing saved inside the blockchain.