I was mistaken about the bungalows! Lothian's Park is in fact a terrace of 6 houses.
In the 1901 census John Lothian is living at The Railway Inn. Scroll back a few pages (from 7 to 4) and you will find Lothian's Park. Do the same in 1891 and Lothian's Park isn't there. Even allowing that the enumerator might not have travelled the same route, I'm fairly certain that it doesn't exist, as an adjacent street, Bronwylfa Square is present in both years.
I've also found a map in an old book on St Asaph's history, which shows 2 fields to the rear of the properties on Chester Street, i.e. where The Railway Inn was. Written across the fields is Lothian's Park. The map isn't dated, but the book was published in 1898.
My guess is that John Lothian owned the fields on which the terrace was built, some time between 1891 and 1901.
Hope this is of interest.