Sigh. The stock photo they pulled for the article is a PC Jr, who's 30th birthday won't happen for another two and a half years. Come on, folks. If you're going to write this stuff at least get the details right and don't hand it off to a 22 year old intern who's never seen such a device.
The source code to the BIOS was printed in the back of the tech manual. Only later would people be sued for having read it, and then implemented it again.
Early clones were using direct copies of the BIOS, not merely reimplementing it. The same was true of the ROM code in a bunch of contemporary Apple ][ clones. That sort of thing is never OK, even in free software communities.