The uniform style will differ, one would expect it to be so, but they are both wearing jodhpurs.
The Observer is an officer, his rank clearly carried on his cuff and he wears the leather belt (a Sam Brown ?) to which his side arm is attached. I believe that early on the RFC did not have a uniform distinct from the Army or Navy and was in any case formed out of men already in one or the other who wore those uniforms in the first instance.
George Freeman is other ranks, he wears no belt for a side arm (this is a semi formal photo he would not have been in appropriate uniform without it), his rank would be on his upper arm for an NCO, or forearm for a Warrant Officer. This was at a time of a very class conscious society their uniforms differed and they wore the symbols of their status.
My grandfather's photos in 1913, 1917 and 1919 show him in a uniform jacket just like George's. His sister is photographed in 1919 at the Royal Artillery Ordnance Depot in Chatham stood behind a whole rank of officers dressed just like the Observer. I don't have anything scanned to show what I mean.
I think I agree with lanyard description as it appears to dissapear inside his top left pocket. However, if one googles "aiguillette" and goes here
http://en.wikipedia.org/wiki/AiguilletteIt identifies an interesting point about aiguillette and other ranks in the Household Cavalry - but it is talking about now and not 1914-18. This was the war that ended the role of the cavalry charge on horse back. George re-enlisted, so he could have been cavalry or a dragoon of the old school which is why we see the lanyard/aiguillette and the jodhpurs. Loosely linked but how credibly I don't know.
Happy hunting
Canuc