Alert generation on backfilled tasks causes duplicate alerts to be created so we need to prevent that.
Here's a task which was triggered by one of the sheriffs: https://firefox-ci-tc.services.mozilla.com/tasks/Rj7eE69WRiuaNX4IT3kzIA/definition
And here's a task which was triggered by the bot: https://firefox-ci-tc.services.mozilla.com/tasks/VpZ0nEzzTFOLRuwAV3UqpQ/definition
The only thing I see which differentiates the bot from a sheriff is the clientId field. However, we can't find this field in the Job schema which is needed to decide if we should trigger alert generation here: https://github.com/mozilla/treeherder/blob/master/treeherder/etl/perf.py#L270