I don't know what to even think anymore

So my boyfriends phone was on charge and his alarm was going off but he was asleep. I wanted to turn it off because it just kept going on snooze but then found he has the "secret calculator" app which basically looks like a normal calculator but you can type in a password and things come up that you don't want anyone to see. I asked about it and he totally flipped out and swears he doesn't know what it is or how it got there. But seriously why would he have this .....