However, my reading of the MDs reply based on seeing similar from organisations I've worked for is "having talked to my legal department, I believe the facts are not as you state them".
That was certainly how I read them. That is, that the MD has quite possibly had the security bod's manager interview them and they are alleging something other than the account on here, e.g. that the lad ran up the whole escalator, his friend wasn't there at the top or perhaps he was abusive.
I'd certainly say, given this, to make it very clear to the son that lying to a Court is a very, very serious matter indeed, and thus if the story he's telling isn't quite the truth (which is possible) then now is the time to come clean, because if he did lie to the Court and was found out he could be found guilty of other far more serious offences such as contempt which can carry a prison sentence, and because changing the story on the day would not be looked upon kindly. If this is the case, pleading guilty is probably the best option, particularly as a Byelaw offence doesn't carry a record as such.
It might be that he said something he didn't consider to be consequential, such as a dismissive "oh, f*** off", which has been considered to be abuse, perhaps?
It might also be that the security guard is about to commit the same offence of lying!
It's bizarre, to be honest, that if a misconduct offence is being alleged in this way, that the CCTV and any bodycam footage isn't automatically retained, as that would be totally conclusive.