Ok thanks. In reality there is nothing you can do which will guarantee that they will not dismiss him. If they wanted to they will, no matter how much resistance he puts up.
If he is being accused of doing something which is commonplace, then he should try and point out that he is not the one who does it, however it will not really be a defence if he has clearly been told this is against the rules and he knows he should not be doing it.
The main positive here is that he has been working there for more than 2 years, which means he is protected against unfair dismissal. Therefore if he believes he should not have been dismissed he can challenge the employer over it. It is a free claim so the risks of taking it further are relatively low and whilst he cannot force them to take him back, he can get compensated.
For the time being he should defend the allegations as best as he can and hope that they give him another chance. I do not see anything that stands out with the procedure so far which would give you a strong argument that this is flawed so it would come to the employer and what they believe should happen. As a saving grace he could ask for further training to ensure that he does not do things he should not be doing and improves his performance.
However, if this does end up in dismissal he can initially appeal to the employer before considering whether to claim for unfair dismissal in the tribunal.
Does this answer your query?