On an online typing tutor site I came across the following phrase:
We're now going to move on to words who's first letter originates on the top row.
Can "who" normally be used in this way (to refer not only to people)?
Well, no. The sentence which you quoted must be a typo of:
for the following two reasons.
The relative pronoun “whose” can refer to non-living beings.
As an aside, I doubt that “(whose) first letter originates on the top row” is a usual way to state that the first letter in a word is in the top row of the keyboard. However, I will not try to write more about it because I am not completely sure and this is not the topic of this question anyway.