People also get better naturally, and with game reps.
That was his first start ever, in primetime, island game, at Jerry's world. And it's not like he had to press, the game was 100-3 basically after the opening kickoff.
Not saying Brady didn't help, or isn't a good coach, etc. But Burrow was good enough to be recruited to Ohio State, he was good enough to get re-offered to go to LSU, and since he left Brady, he's been absolutely sensational. Dude is just a baller, period.
Also, you could see the light starting to come on about halfway, maybe 2/3 through that 2018 season. He was starting to look like a really good QB by the end of the year. There's a reason a lot of folks were on him 150/1 to win the Heisman in 2019....it's because of how he looked towards the end of 2018.