Mary,
George Boyd is a fairly common name in Co Down. In the 1901 census there were 53. You really need to try and get your George’s parents names from perhaps a marriage or death certificate, otherwise there’s no way of being sure of finding the right family. And if you can narrow the search to a townland or parish that would make a significant difference too.
Your assumption that George may have been an Ulster Scot seems reasonable enough. Over half the population of Co Down are of Scots descent and that is often signified by being Presbyterian. It was Scots settlers who brought Presbyterianism to Ireland and it’s the largest single denomination in Co Down to this day.
You have put this query under Newtownards but then say you don’t know what parish he came from, so I assume Newtownards is just a guess. (If not, I can advise you on what church records exist for that parish).
There are plenty of Presbyterian churches in Co. Down, perhaps 150. Not all have records for the period you need but some do. They are not all on-line and to check them you would have to go to PRONI (the public record office) in Belfast where the records are on microfilm.
This is a link to a Co. Down site with a lot of Boyds on it. You might find it helpful if you can narrow the search to a specific parish or townland:
http://freepages.rootsweb.com/~rosdavies/genealogy/SURNAMES/B/BoydAJ.htm