During their conversation, Lin Zheng's match, which is Group 3, had already started the second round. From the way Lin Zheng drew his tiles, it was clear that he had some level of proficiency. He was not like a Mahjong novice. Moreover, Qian Cang Yi noticed that Lin Zheng had started to count tiles.
Mahjong, essentially, is a game of strategy.
In this competition, there are only 108 tiles in total. Since there are certain combinations needed, when playing tiles there will inevitably be choices. For example, compared to the '3-tong' and '7-tong', the '1-tong' and '9-tong' are obviously of lower weight, because the former can form sequences on both sides, while the latter can only do so on one side.
To form a winning hand, unless there are other intentions, in the case where there are '3-tong' and '9-tong' tiles in one hand and both are single tiles, people generally discard the '9-tong', which is considered an 'edge tile'.