Many companies use "open source" or simply "open" in a way that isn't compatible with the open source definition. This is known as open washing. A good, non-Microsoft example is Epic Games and Unreal Tournament 4. They talk a lot about being "open", but the source code and assets are all proprietary.

Neither Epic (I've contributed to UE) or Microsoft assert their products are Open Source, merely 'open'.

And they do that explicitly to confuse people. What they do isn't open, it's smoke and mirrors.

Actually I think only MS say open. Epic says free.

Microsoft in particular has a history of using "shared source" licenses that are not free.