I don't understand why you've mentioned "on the screen".
If the treshold is set too low, we'll end up with false positives. I.e. we'll think the study shows something when in fact it doesn’t. And this is not something that can be fixed in follow-up papers.
It was a genome wide screen looking for synthetic lethality with another gene. As with all screens you get a bunch of hits and you follow up on the most promising ones, which they did in the paper.
If the treshold is set too low, we'll end up with false positives. I.e. we'll think the study shows something when in fact it doesn’t. And this is not something that can be fixed in follow-up papers.