Yeah, it's probably similar to Puzzle and Dragons, where your action have absolutely *no* bearing on what drops.
It's actually the only way they can do it without people cheating - when you enter a level, the server sends the game the information about what monsters are spawned, which drops, what they drop, etc.
Otherwise you could technically run cheats (well, you still can to make yourself invulnerable, for example, since I doubt that the game communicates with the server after every turn you do) and force the game to drop exactly what you want.
I'm sure there's analytics that the game has that log what happens so in case you're cheating they'll know (they can very easily track how much damage has been dealt, how much has been healed, etc) so that they can know without an ounce of doubt that you've been cheating.
We'd need someone to packet sniff what comes in (like someone did for PAD, which is how we got the information) to determine what is fixed and what isn't.
Speaking of cheats, the absolute only effective cheat I could see for this game is something that guaranteed sparks with extreme precision - if the cheat knows what characters you have and has data about how their attacks are performed, it could pretty simply determine the optimal order and timing to perform the highest amount of sparks possible and just do it for you by sending taps to the application.