I believe GitHub was able to tell which public keys had been added using this exploit (because with this vulnerability, the log files should still be intact). S

I believe GitHub was able to tell which public keys had been added using this exploit (because with this vulnerability, the log files should still be intact). So we/they can safely say that this vulnerability was not exploited maliciously. Sure, there may be others we haven't heard of, but that's potentially true about any service.