Right. The alternative would have been to fix it only moving forward in which case you're left with a bunch of guys with artificially inflated numbers compared to everyone else because they were grandfathered in which makes the overall system less meaningful.
Yes, the most important thing for the recalculation was that everyone was even when compared to everyone else.
In other words, the counts before were not correctly proportional compared to everyone else. Now they are even across the board making for an even playing field for everyone.
Thumbs up is your total score (some members thumbs up click will be worth more than 1 point based on their own score and you get 10 off the bat).
Received is the total thumbs clicks as if they were all only worth 1 point.
Unique Thumbs is how many unique members clicked a thumbs up for you. If they did it more than once, it's not counted again here.