From the bottom of the article under "Origin of the File":
The source was posted on the Korean-language blog
6502.tistory.com without further comment, in a marked-u
format:...
[ lots of interesting background here ]
...
Given all this, it is safe to assume the file with the
Microsoft BASIC for 6502 source originated at Apple, and
was given to David Craig together with the other source
be published.
So my guess is potentially safe to look at, but that's about it. If you have any doubts, I'd recommend not reading the original post.