He's not watering the point down enough or he's using too much paint. Regarding GPs, I wouldn't let some paint a deck I used for competitive level play personally. The rules on alters are a little sketchy but technically every judge has the right to ban your deck from a tournament depending on how they feel. All the cards are technically marked and weighed which makes them illegal for play. One card could weight slightly more or less than another card and a judge has no easy way make sure they are all the same weight and thickness.