I'd say the first author didn't do his due dilligence.  The second author was reassuring the vast majority of people who don't tell itunes to overwrite the music on their server.

The second author only ever discussed what happens on the primary Mac.  He implies some of the things that happen on secondary devices -- including a second Mac -- but if you read carefully, nothing he says rules out what happened to the first author. 

By all means, I agree with you that the first author shouldn't have installed Apple Music on his DAW without being intimately familiar with all the ramifications of doing so, I certainly wouldn't. 

But the second author is obviously just an Apple fan, trying to reassure people without actually saying anything.  Personally, people like that just make me more wary.