It also seems like it trained on dialog in plays and novels. Some of these responses seem way too "perfect", like a response you would hear in a dramatic soap opera. Honestly it might be using that too. Just my take from listening to first minute or two of dialog.
The NSA has a much better training set.
Telephone conversations are quite different from in person speech. The lack of visual cues from the face, or the lag in video chat, the echo cancellation and the quantisation and comprehension, all reduce the quality subtly.
Now the Stasi archives, that would be interesting. Sometimes people suspected they were being surveilled of course.
Likely audiobooks too, which certainly wouldn’t help the dramatic tone.