Can a Site Collection contain another Site Collection?
If you have an answer, please give also an authoritative source of information.
The answer is simple. No, by design.
SharePoint is not designed to have site collections under another one.
Even if on-premise it “can” be possible by using a tricky way with managed path which is not recommended at all.
As authoritative documentation, I think at the same page you took the picture here: Plan Site and Site Collection in SharePoint Server
Site Collection can not contain another Site Collection.
SharePoint Site Collection, just as the name implies, is a collection of SharePoint Sites. Each site collection contains a single top-level site and subsites below it.
You can have multiple site collections within a single web application, a single site collection can contain a number of subsites within itself.