Looks to me like they would block the original battle result data packet and replace it with a spoofed one, which is definitely not impossible since the client only gets the RNG seed, but the calculation of the battle and its outcome is done on our devices.
Best way of countering this would be to add an additional enconding layer using the exact timestamp of packet creation, since it could be very easily deduced then when the time between battle start and result generation was definitely to short to be genuine (like 15 seconds for a coliseum win where already the team walk-ins and switsching time between the 3 battles easily adds up to this time span)
But till countermeasures like this are implemented those guys surely need to be banned permanently (though maybe not immediately, since it certainly would be a good idea to monitor them extremely close for some days prior to this to find out the exact ways of how the accomplish this since the way I described surely isn't the only way that could be done)
Please don't bash me for voting to let them continue with this for some more time, just consider this: If they managed to do this and will simply get banned, even if they would stay away from the game there would sooner or later be others using the same exploits to do it again. Therefore it is vital to find out how they do it and to prevent the possibility of doing this!