Lone is not a common name in Ireland. There are only 10 in the country in the 1911 census. There is not a single William Lone death 1864 – 1921. The only William Lone in the 1911 census was single, aged 24 and lived in Westmeath.
I searched under Loan and O’Loan which are variant spellings but I didn’t find anyone who fits very well. This man from Co. Kildare was in Belfast in 1901 and is just about old enough to have fathered James c 1879 but his occupation doesn’t fit:
This man married in 1878 as Lone, when he was a fruit seller. Now he’s a grocer. So again the occupation is wrong. (Should be farm labourer).
He died in 1909 when he was O’Loane (the O’ & Mc prefixes on Irish names are detachable and were used or ignored just as folk felt).
There are a couple of trees on Ancestry which have James & Sarah, and they have him born in Portadown, Co. Armagh in 1878. I checked all the births 1877-1879 registered in that area and there isn’t one that fits that information. Nearest I could find was this un-named male, surname Lunn who was illegitimate and born in Lurgan workhouse in 1878. Mother Jane Lunn:
Lunn to Loan is not impossible but I have no real way of checking. It wasn’t unknown for a groom to invent a father’s name and occupation to hide illegitimacy. So perhaps William might be a fiction. A bit of a mystery family I am afraid.