If the lads are following a DB then they can follow the DB till checkmate
if it goes that far.
What may have happened is that one lad has run this game through a top box
and it has found a smashing move. So the lad leads someone along this path
and then unleashes his corker.
It's not cheating in the sense of the word because the lad did not use the
box during the game, but before it.
If questioned and the lad says this is the case then you have to believe him.
Also the chances are you will find a game he played without the corker thus
verifying the fact he boxed it (or burnt some midnight oil) in between games.
A wee bit of a grey area because you are using a box in a postion
you know or hope WILL appear in one of your games.
While a game is in progress you may not refer to chess engines, chess computers
or be assisted by a third party. Endgame tablebases may not be consulted during
play but you may reference books, databases consisting of previously played
games between human players, and other pre-existing research materials.
So you running a box over a previous game and finding a smashing move can
come under the banner of ' pre-existing research materials'
But if the DB you are using has box analysis in it and is therefore not between
human players then.....grey area.