Those are simply the reference numbers of the medal rolls (or registers if you like) in which his medal entitlement was recorded.
The Royal Flying Corps entry is for the 1914-1915 Star earned with the DLI (he seems to have served in 4th and 10th DLI), recorded on the RFC roll, having transferred at some time to that corps. He would, like all RFC men, have become RAF on 1 Apr 1918 hence the remaining record for the British War and Victory Medals being on a RAF roll.
And yes, quite normal to transfer from, in his case, the infantry to the the RFC. The later move to the RAF was automatic.
His detailed service record does not seem to have survived the WW2 bombing.