If it's not legit, then there's no reason to report it. I doubt it's possible to get that much as to overflow the value.
It's legit. I mean I cheated to make it happen, but you can put something to hold down the arrow key and it'll eventually overflow. Would take a few hours but definitely possible.
I timed how long you have to hold it down for. It takes an hour to get 1 million logs. 21 million logs is the highest amount you can have as that equals 4.2 billion gold, which around that points causes the overflow to happen. So basically, it takes holding down the button for 21 hours. Lag happens as the number gets high, but not for quite a while, and for all I know, the lag may just be happening because my computer is old.
Essentially, you can have something holding down the arrow key for most of the day, but it's definitely achievable without using third party tools. Let's say I put the right arrow key down with an object right before I go to bed, wake up, do my daily routine, and then go out for the day and come back. By that time, I'd only have a few hours left to go.
When it comes down to it, 21 hours of holding down a button for 21 million logs and actually getting a payout of 4.2 billion gold is a ridiculously good payout and easily do-able as long as you just have a bit of patience and won't need your computer for a while.