Fidelity Bitcoin

I read on Reddit that BTC on Fidelity is an IOU. I have been reading on it for a while and I thought that that was not the case. I looked for the link of one of the FAQs I read and its here: https://www.fidelity.com/learning-center/trading-investing/how-to-send-bitcoin

So… is it really an IOU? Or are they just essentially a trading platform and you can own your BTC if you want?

Looking for clarity here. Maybe I need to see a factual counterpoint to prove my assertions wrong…

Edit: it appears that this link I referenced is just describing how to transfer BTC, not how to transfer BTC from Fidelity.

Thanks.