This was either written very poorly or lacks serious basis to conclude thoughts about employee feedback (of which drives the thesis of the whole article).
First - "I talked to a lawyer and he didn't think it was a risk", does not sound very much like legal advice. Is there precedence for civil cases that were thrown out due to the basis of "just giving technical feedback"? How often do firms that provide "just technical feedback" get sued and how often do they settle those suits?
Second - I think most people want feedback on "how they interviewed" and not "were they the right fit for the job". This is where you get into a gray area of legality, because anything you might say may get misconstrued as discrimination. "Oh you think I was too nervous during my interview...well I have X condition that makes me like that and you can't reject me for that"
Third - feedback on technical skills? To what avail does this hold for the candidate? Example:
Potential Employer: "You couldn't reverse a string, so work on string reversals."
Potential Candidate: "Ok, I'll go learn a string reversal so I can ace my next interview"
Feedback on interviews is imperfect because the hiring process is imperfect.