What is the best explanation for why a particle is striking point X? Alpha particles are mostly empty space, so they move in random directions, and one of these alpha particles can strike point X.
The gold atoms contain negative electrons, so when alpha particles strike the gold they keep moving but in various directions.
If an alpha particle hits the gold foil, a gold nucleus splits and a particle from it flies out at point X.
When the dense, positive alpha particle passes close to a positive nucleus of gold, the alpha particle repels and hits the screen at point X.