This direct-to-DVD movie was the 4th of 4 to be released after the tv series was cancelled at the end of season 5. When the series was to be revived on a different network, this movie was split into 4 parts, each part equal to the usual length of a tv episode, and shown first as season 6 episodes 13 through 16.
The other 3 movies were also similarly split and formed the rest of season 6, 16 episodes in all. Finally, the new episodes made specifically for tv followed as season 7.
This practice was identically used for later tv syndication and streaming services such as Hulu.