Doddie
Name 'Pension Records' is a bit misleading as they are really just copies of records that were in the hands of the Pensions department, not a full list of those who recieved pensions and in fact your man may be in the surviving WO363 service records, which Ancestry are currently uploading ( only A-C available as yet).
Medal card on Ancestry are also as not fully uploaded ( around about 50% I believe) and your man's card appears not to be on yet, but he does appear on National Archives database of mdal cards
Medal card of Stewart, George J
Corps: Cameron Highlanders Depot
Regiment No: S/32166
Rank: Private
1914-1920 WO 372/19
Alan