Tbh, if you suspect he has just fobbed you off - that means he's unlikely to ever call you - so what harm will messaging him do?
Its not like one email after 4 months is hassling.
You 'might' catch him at the time he needs someone and faces the task of wading through past applications and he may be glad you've appeared. Its always hard to say how others will respond to things like this = but its highly unlikely to *** him off, so no harm done.
You could even add that you know hes busy and you dont want to interrupt - you hope he doesnt mind you keeping him updates = and maybe even something along the lines of, no need to respond, if youre really worried.
if nothing else it shows you really like the company etc - and that youre not just firing off cvs at random
but basically filing you away for the future is a common fob off thing to say - although some do actually do use them