That doesn't specify how many bugs there existed in the Discord codebase throughout the time where this person was active. Only once you know that, can you say

That doesn't specify how many bugs there existed in the Discord codebase throughout the time where this person was active. Only once you know that, can you say whether they found a significant proportion relative to the effort they've spent and would spend as a part-time employee. That other people still find things also suggests that the statement above ("just hire him and you're secure") might have been a bit simplistic