In my opinion verbally abusing an ex-soldier regarding his past employment is inappropriate, as with any verbal abuse.
There is no suggestion, and I find it highly unlikely, that the sacked person knows the ex-serviceman or his career. However, he is said (and claims) to be a "veteran" - of an armed conflict, one assumes. The implication is that his participation was in military conflict within the last 38 years. Unless I am confused, only two of these involved (official) UK soil (invasion or direct defence/policing) - Northern Ireland and the Falkland Islands. The rest all involved the UK sending its forces to fight abroad where the UK was not under military attack or in a state major civil conflagration.
If the ex-serviceman fought in the first two then the abuse was at least inaccurate. If in any of the others, then it may have been correct but nevertheless uncalled for.
I would not agree with the quite common assumption that an ex-serviceman has sacrificed anything "for his country", he applied for a job, got it and (one assumes) did what was expected of him. On leaving his job he would appear to get certain privileges, which he is entitled to claim. I find the modern "hero" label applied in blanket fashion an entirely inappropriate jingoism.