It would be nice if more horns were used that way or a friendly hoot to say 'hello I'm here' but because the vast majority are an aggressive 'Get Out ta Way' etc people often react negatively to them and situations are escalated
Notwithstanding that this instance
may have been intended as a rebuke, which is mis-use of the horn and unwise due to being seen as provocative, the UK attitude to horns is decidedly unfortunate, as well as not in keeping with the Highway Code, which specifically suggests the use as a warning of 'I am here'. Having just cycled the length of Italy, I was surprised and impressed that it's very common indeed in Italy to give a brief, non-aggressive horn sound / blip to signal presence, particularly when about to overtake. It would be excellent if people did this in the UK. Unfortunately, it seems to be seen as aggressive by just about everyone here :-\ Perhaps Italian cars have this secondary horn
@winjim mentions above? Perhaps Italian drivers are actually taught to use the horn this way in driving lessons too?