Gas lighting was introduced across Dublin in 1825 [i] two years after it had been adopted in Belfast [ii]. When the hero says "from Belfast to Dublin…I came" he is presumably referring only to his journey.
References:
[i] Meehan, Patrick Dublin Historical Record Vol. 5, No. 4 (Jun. - Aug., 1943), p135
[ii] Culture Northern Ireland website https://www.culturenorthernireland.org/features/heritage/belfast-gasworks (accessed 11Feb21)