A good refutal of the for-coders claim would be that it's one of the default image editor most commonly included with major Linux distributions. That's a much larger thing than it being just made for coders.
Yes it does because ZeMarmot producers are the main contributors to Gimp's code.
ZeMarmot's announcement was in 05 February 2015.
The GIMP was an at least 17 year old software project, when the animated movie was announced.
Of the two main GIMP maintainers, one of them works on ZeMarmot.
What this all says is that yes, there is an animation movie 10 years in the making, by some of the people who also work on the GIMP project. It says nothing about GIMP being made for any particular purpose, either or not for coders, and/or for animation or for visual creatives in particular.