Just few comments based on my interpretations (not necessary more correct):
Anthropomorphism: as apple moves, you attribute intentions and feelings to it - now it flees, now it gave up and so on.
Determinism: you start out as usual trying to control the snake, but very quickly realize everything is predetermined and your sense of control is illusion.
Monoism: we are all part of oneness, you are devouring yourself.
Nihilism: I especially liked that you cannot go back to menu, you have to refresh the page. It's kind of a dead end in terms of meta-game (game of games).
Optimism: The reason you are not growing is that would make the game more difficult. You stay forever a child.
Anthropomorphism: as apple moves, you attribute intentions and feelings to it - now it flees, now it gave up and so on.
Determinism: you start out as usual trying to control the snake, but very quickly realize everything is predetermined and your sense of control is illusion.
Monoism: we are all part of oneness, you are devouring yourself.
Nihilism: I especially liked that you cannot go back to menu, you have to refresh the page. It's kind of a dead end in terms of meta-game (game of games).
Optimism: The reason you are not growing is that would make the game more difficult. You stay forever a child.