I'm pretty sure he just showed up to a store and said "how do I play" and then won a box.
The funny thing is that you're not too far off. The old rainbow bogles list I paraded around is something I just made up not really knowing anything about modern. I'd never watched a game of modern before, so I started showing up to a local proxy tournament in a shed. First I made up a random deck based off cards I liked by just googling bant cards(which led to me accidentally building mythic conscription not knowing it was an established standard deck), which did ok. Then looked at one top 8 list, and I printed out bogles and sleeved up on location. I got 2nd place and some packs and decided I liked it because I didn't have to know what my opponent was doing to win, so then I went on cardkingdom and just typed in effects I wanted in the advanced search for hours until I came up with the rainbow list. I learned a lot by pretending I knew how modern worked and just sitting back with an uninteractive deck talking with the people in that shed(there's also a funny story involving dropping keys in a port-a-potty, but that's for another day).
Months later after deciding to join modern I went back and ordered the whole deck for like 250 bucks.
Then I showed up with it to the LGS win a box as my first modern sanctioned tournament and won two weeks in a row. Basically every deck I played against was the first time I had ever seen the cards. Fuck if I knew what creatures were in a pod deck and the only thing I knew about the
Scapeshift deck I played in the finals the first time was that I overheard some dude talking about keeping your lifetotal above 18 at the shed tournaments. I made up a bunch of justifications about beating Treasure Cruise Delver and such, but the reality was that I just liked the idea of playing 5 colors and wasn't very confident in playing Modern and having to make decisions.
I think these sort of experiences really shaped the type of player I am. Every time I see someone's losing reaction to a card I chose, it makes me want to play more. The sense of discovery and creativity I get from digging through the thousands of cards in Magic's history and then winning with my picks is the reason I play magic(and why limited is the best). Even back at that first FNM with my mill deck, I didn't win the tournament but I did beat the best player in the shop and that's what really got me going. And recently, doing well at both of the pptqs I entered with my sultai eldrazi deck after mediocre results with relatively stock Jeskai Black really reinforced that that's the player I want to be.
Sorry I wound up rambling a bit lol