I LOVE the warrior series and I just reread the first book. I forgot how much I love Firepaw and Sandpaw. I know that they don't get together in the first book, that they hate each other but I love them later on.
They are similar but obviously not the same. Anyone who has seen a cat lay down like that(and has the artistic skills) could get the same pose. There are major differences in style and the poses aren't even completely the same. It would be like saying someone who has seen the lion king and draws a lion roaring, even if it is in a completely different style, stole their picture from Disney.