Sounds like bull to me, probation period, despite popular belief, doesnt mean that can fire people without good cause. Many of the laws protecting workers apply to those on probabtion too. There should be greivance/disciplinary procedures laid out in your employment contract, if those werent followed, you might have a case for wrongful dismissal.
Pointing out your holiday leave as proof of your disengagement is laughable, when you were trying to get more work by asking your manager! Sounds like they missold you the job in the interview, and didnt like being questioned.