You phrase it as if in Bitcoin Core, users have no control over private keys and that this wallet is not open-source in the usual sense but is something more than a bitcoin wallet, sacred and mythical like a decentralized entity that exists outside comprehension and sway of human beings.
If that's what you thought, then you misunderstood what I said.
No, Bitcoin Core is not "decentralized" because it is just a piece of code that behaves identically on any computer which runs it. It should behave identically and enforce the same for all rules because this is how consensus is being achieved. Decentralization is a distributed process by means of which people or software come to an agreed-upon truth. Truth doesn't need to be "real" truth; this truth is only applicable to a system where it is being found through the painful process of achieving consensus. Bitcoin Core, however, is decentralized in a different sense: the process of development distributes among thousands of participants, and there is no particular person or group who can dictate what to add or remove from the code.
Pretty much, I called it "decentralized" in a way that no one sole company/entity is in control of the software development. As for the others, you're probably over-analyzing my 3-sentence reply.