This thread seems to be drifting around a bit. If it helps, here is a bit of info about the assignment of RTF frequencies. In the UK almost all aircraft service frequency assignments are technically for communication between ground stations and aircraft stations. You will often find this referred to in the rules as air-ground-air or AGA.
Communication directly between aircraft stations is not part of the licence conditions so, technically, except in those situations where we break the rules for safety reasons, pilots should not talk to each other directly.
These licence conditions are largely derived from the International rules set out by the International Telecommunications Union - a United Nations specialised agency for information and communication technologies - which means they should be very similar in almost all countries. However each country has to put the rules into its own law and this introduces differences.
Almost all frequency assignments in the aviation communication band are for air-ground communication. The use of the frequency to provide an air traffic service (ATC or FIS) or the UK's Air Ground Communication Service is authorised under different rules and is associated with specific frequency assignments.
So, the man at Seething was probably technically correct to say that the OP should not have called the other aircraft directly but as many others have pointed out we will have to be sensible about the way frequencies are used.