"Britain was initially taken by surprise by the Argentine attack on the South Atlantic islands, despite repeated warnings by Royal Navy captain Nicholas Barker and others. Barker believed that the intention expressed in Defence Secretary John Nott's 1981 review to withdraw the Royal Navy ship HMS Endurance, Britain's only naval presence in the South Atlantic, sent a signal to the Argentines that Britain was unwilling, and would soon be unable, to defend its territories and subjects in the Falklands." (from here.)

It's possible that this was just stupidity on the part of the Thatcher government, and that there was no intention to send the generals such a message. But the alternative possibility cannot be dismissed out of hand.