If you give him an inch, he will take a mile!
If you let your policy framework be too flexible, the flexibility can kill you!
Its like saying: I broke a traffic rule, but hell didn't break lose... Well, buddy, our traffic conditions are pathetic just due to this attitude and the stress levels while driving, the number of accidents and deaths and the overall transport cost far exceed Europe... where your minor offenses are recorded and punished severely.
The HR manager inducting has to do it efficiently. One cannot expect him to keep following up with guys after joining. Its not a good practice. He has other work to do than load his staff with this petty joining formality.
That being said, a colleague posting that saying that he was wrong, is construe-able as a defamation exercise. Being a lawyer as well, I would urge the moderators to help sensitize the person on such consequences.
Every issue should be professionally treated and the understanding of those words vary a lot with the receiver. However, bringing in that objectivity is probably the task of the top management.
Lastly, A class men recruit A class men... B class men recruit C class men... So, if one is pushing the limits here, Mr. Y will not be the only guy in the limelight (assuming he is wrong, which cannot be proven here anyway).