Of course I cannot be sure about this, but I do recall there was a lot of talk on TMO about this before Jolla ever came out with the device specifications.
There were a lot of people who stated that their preference was a device with full HW-buttony qwerty keyboard, and when the specs were published were loudly wailing about it and vowed not to get the device.

There is some possibility that at least few of these people would change their mind when the TOHOKBD2 campaign started and would have ordered both the keyboard and the device with the accompanying coupon.

And if not, I sure think that'd be the target audience.