I did, in fact, read the link, and I'm reacting to the condescending language used throughout. The unspoken attitude in the article is that the employee is a dirty traitor and a fool for wanting to move on. 'Shields down' is a telling choice of words because the manager feels that the employee is protected by being his. It's a patronizing, parental sort of attitude towards employees that irks me to no end.

To pull another quote:

  "If I’m sitting here talking with you it means two things: I don’t want you to leave and, to the best of my knowledge, you didn’t want to leave either but here you are leaving."

Here he's either assuming he can read the minds of his employees, or that his employees should share every dissatisfaction and stray thought with him. Hyperbole, perhaps, but not by much. I don't want a nosy dad for a boss.

The problem is with the implied meaning.

Calling this mode "shields up" implicitly means that it's something good for you, protecting you - but it's not quite so, this "shield" is protecting the company/manager instead of you. The exact same thing might be called not "shields up" but "complacent mode" or "ignoring opportunity" for the opposite implied evaluation.