For a different London cemetery in a slightly later period I found:
- Brought From - The place of death; could be hospital, hospice or home address.
My first thought was that Hoxton Square might be where he had been residing so I checked Land Tax Records on Ancestry.com.
I found that John Smyth was living in Holywell Street (now called Shoreditch High Street), which is within a few hundred metres of Hoxton Square, for at least the years 1786-87, 1797-98, 1800-02 and 1804-06. During the last 2-3 of those years the heading in the records book (a few rows above his name) which had earlier been Holywell Street was replaced by just Street.
I suspect that some confusion over street (re)naming may have led to whoever brought his body to Bunhill Fields deciding to use the nearest well known landmark (thought to be one of London's oldest squares) rather than his home address.