Earlier quoted context omitted.
The two examples given in support of short local variables names rely heavily on convention or prior knowledge. I don't think they're strong arguments for making short variable names. Naming the integer counter "i" is convention learned in CS class (initially) that has become common usage. If you have nested for loops then j, k are often conventional for naming the next counter variables, though without an enclosing…
Relying on convention is a good thing, as long as your team (and the larger community for that language) is mature enough to have a strong set of relatively easily discoverable conventions.
I'm not saying convention is bad, I don't think that at all. I'm saying that the two examples here aren't good advocates for a general principle of short local variable names. The examples work only because people already know what they mean, due to the pre-existing conventions.