The smaller key appears to have much more wear on it than the ignition key. Since you use the ignition key every time you use the bike the only way I can think of that the smaller key would show more wear is if it's from another bike. My guess is that you are not the original purchaser and the person that you bought the bike from left the key from a previous bike on the key ring when he sold you the bike. If you are the original purchaser and don't know what the smaller key is for then how did it get so worn? This isn't a trick question from you is it?
John