They haven't awarded themselves a bounty.
If you hover over the bounty indicator in the margin of the answer (it says something like +50), you'll see a tooltip that indicates who awarded the bounty:
In the case of this recent question, for instance, Tintin's answer was awarded a 50 point bounty by the user Rizvan. The revision history for the question itself indicates that Rizvan started a bounty on the question on March 19th, and the bounty ended 3 hours ago.
Same thing with this question; Rizvan set a bounty on the question and awarded it to Tintin.
Those are the only two bounties that Tintin has earned.
Perhaps the crucial element that you were missing in your understanding of the bounty system is that users can establish bounties on other people's questions?
In response to your edit: Why does that seem weird? There's not enough evidence here to establish a pattern of abuse. It's likely that Rizvan just does similar types of work as Tintin, and therefore has similar questions. If this happens again, then it might be time to do some closer investigation.