This was the first episode produced in 2003 according to the credits.
In addition to being the first episode produced in 2003, it was also the first episode to premiere in 2003.
This is the first episode of the series after Craig McCracken left to work on Foster's Home for Imaginary Friends (2004) where others such as Genndy Tartakovsky and Paul Rudish went to work on Samurai Jack (2001) in the show's previous four seasons and The Powerpuff Girls Movie (2002). However, Lauren Faust was a supervising director in later two seasons when the series first aired.
This is the first episode of the series where Chris Savino took over as a showrunner in seasons 5 and 6 which did a previous show for Dexter's Laboratory (1996) in seasons 3 and 4.
This is the season 5 premiere of the series.