When you need to bring up article 63 and 69 of the Grundgesetz to prove that the claim is ludicrous, maybe the reasonable thing to say instead is "I understand why you might think that".
I don't think it bungled it and I don't agree that there's a clear ground truth here. Quite the opposite: you've only convinced me that the semantic ambiguity is real. It's like debating whether interim CEOs should be included in a list of CEOs.
You are, of course, free to ignore German law and its definitions, but that doesn't change the fact who actually was a Chancellor and who was not. Chancellor is a very well defined role.
I honestly don't understand why in situations with a clear ground truth there is a need to debate and why we would want machines to bungle that.