A batsman gets bowled out when the bowler manages to hit the batsman’s wicket. This could also happens, when the ball is reflected by the batman’s cloth or pads.
Notice, the wicket has to break, so the bails have to fall down. Otherwise the game will continue and it is not rated as a bowled out.
Also to notice, it does not matter if the batsman is standing on the bowling crease or not, the batsman will be out if the wicket breaks.