[dmch-1]

Perhaps being recorded was a big deal back then. So they made more effort. Today it is common to have ones speech recorded, even for mass media.

[pmezard]

One of the highlighted characteristic of this recording, is it is a live conversation, not something rehearsed.

So, while what you said may be true for radio broadcasts, I am not sure it is at play here even if the interviewee knows he is being recorded.

[alricb]

In 1912, the recording equipment would have been quite conspicuous.