Even with his gumpian version he still didn't understand the concept of percentages. 3 is 60% of 5. So technically it would be 40% more DBs from UGA in the NFL as opposed to Tennessee. 100%-60%=40%. Bottom line, hopefully someone is managing his money for him.
He based it off of a 166% increase from UT to uga. Your example is actually incorrect because you are only factoring in those that made it in and leaving out the rest. 30% of UT dbs make it to the nfl if 3/10. 50% make it in if uga 5/10. That's a 20% better chance out of all dbs. If you only count those that make it to the nfl it is a 40% chance difference as you stated. If it were based off of increase from ut to uga, it would be a 166% increase (3 vs 5) but would be a 40% difference in chances for successful dbs only.