Being an escaped POW sounds precisely the sort of circumstance in which he might have got an emergency passport. He would obviously want to get back to the UK or Ireland as quickly as possible. Getting a new full passport would have required a birth certificate etc from Ireland and would have taken months in wartime. Whereas the Consul had/has the discretion to issue that one-way document without further enquiry, and evidently used it.
Regarding birth in Kilkenny, the obvious question is was it the town of Kilkenny or the county?
Church of England, in Ireland, is the Church of Ireland.
If it was the town of Kilkenny there are 4 churches there, and their Church of Ireland birth, marriage & burial records have been copied for the following years:
Kilkenny Garrison 1920-1921 -
St Canice’s Cathedral 1790-2016 1790-2007 1790-2016 Some coverage at RootsIreland.ie.
St John 1890-2016 1845-2005 1845-2013 # Earlier records destroyed in 1922. Some coverage at RootsIreland.ie.
St Mary 1729-1935 1729-1942 1729-1952
The original documents are in the RCB library in Dublin (Churchtown, Dublin 14) but 2 of the parishes are on rootsireland (for some years). I’d be surprised if 1918 was on rootsireland, as they tend to focus on older records. The RCB library doesn’t do look ups, as far as I know, so you would need to get a Dublin based researcher to go there.