That article is a bit confusing because it's using the term "BASIC" to refer to both the language and Microsoft's implementation. But what it's trying to say is that Microsoft's BASIC implementation was licensed by many computer companies (including Commodore and Atari) and that those companies changed and extended it in incompatible ways.

That's not what that says at all. It says that the language was slightly different depending on the platform.

Microsoft basic wasn't the first basic interpreter which is a different claim than Microsoft basic source was copied from another interpreter.

What part of that paragraph you quoted suggests that Microsoft BASIC wasn't original work?

Those were their own ports, as per the page you just linked. They developed Microsoft BASIC.

"The Altair BASIC interpreter was developed by Microsoft founders Paul Allen and Bill Gates using a self-written Intel 8080 emulator running on a PDP-10 minicomputer."