The 24-year-old striker made his second debut for the Cumbrians in their goalless draw against Crewe the same evening.
Garner left the club to join Nottingham Forest in 2008 before moving to the Hornets in August last year.
"I spoke to a few different clubs and when I heard the manager (Greg Abbott) spoke to me and gave me a ring and I was just happy to come back," he told BBC Radio Cumbria.
"I don't think it was just the manager, I think I like the place really, I think the fans are really good and the people about the place, that is another thing about why I wanted to come back. It is just a normal place really, a nice place.
"To be honest I don't really know what things are back at Watford, I have been asked to come here and play for a month and that is what I want to do, and I think the future will take care of itself."