NO.
Most all adults, which is what James Cameron is, are too wrapped up in their own work to bother with blatantly using some other work as an outline in a complete and total act of plagiarism.
Plagiarism is an issue for the school type people SO THEY DON'T BLATANTLY COPY AND TRY AND PASS OFF AS THEIR OWN.
C'mon now...
26 letters in the alphabet(A-Z)
only 10 unique numbers(0-9)
10 or so genres(drama, suspense, action, adventure, sci-fi, fantasy, romance, comedy, animated)
only around 9 basic colors(black, blue, indigo, violet, green, red, orange, yellow, white)
5 senses(sight, sound, taste, touch, smell)
2 sexes(male, female)
and well let's not forget the ole saying "it's all been done before"
Not a stretch that things will look similar. ESPECIALLY when you know how things work and realize that it is very possible that the work James Cameron was doing on Avatar simply paved the way for this other thing.
It's been my experience that the one leading generally does not get to the goal first but when it does it shows you why it's the actual first. The one feeding the other lesser ones, in this case Avatar, gets the praise because it did not plagiarize.