In fact, some people just grabbed their emulator (or some Action Replay physical adapter) to unlock Swim early and went to check the truck… nothing. French-speaking website Pokelord (launched by Mr Bibou) was pretty efficient at checking those rumours.
I heard some other rumour to name your character “Mew” or “New”, some friend tried it… no success.
Until the much later confirmed Mew glitch was discovered (https://bulbapedia.bulbagarden.net/wiki/Mew_glitch ).
I remember the thrill of believing in a glitch, although the strongest feeling I had was not on Pokemon but on Zelda: Link’s Awakening and the Screen Warping Glitch, that would allow you to jump to the other side of the screen by pressing Select at the right time. I was so eager to try, I immediately ran my emulator and pressed Select when changing screen… which did nothing. I was upset, and even contacted the admin about not posting unverified hacks. They even apologized.
I swore I would not believe anything that was said on the net, esp. something so powerful, without having some proof or checking it myself.
Years later, after learning many more glitches on Zelda and Mario 64 contributing to speedrunning, I got curious about the Screen Warping glitch again as it didn’t seem that impressive anymore compared to the crazy hacks you can do in the other games. So I checked it again, this time we had videos, and indeed, it was working! I simply didn’t have the right timing (and I didn’t have TAS on my emulator to use frame-perfect input). I’m sorry for the admin!
Back to Pokemon, another glitch was the Safari -> Bug City, which was easy to confirm. But I found the reproduction steps far too complicated (go back to the cabin, look at the poster, then move down…). I got the intuition that only a few key steps contributed to messing up with the game’s memory, so I tried to find the “minimal reproduction” (a term I only learned much later when becoming a developer), the minimum steps required to trigger the bug. So I could explore different kinds of Bug Cities much faster. I’m proud not to have just blindly followed the steps found on the Internet but actually identified the right triggers (if not what actually messed up memory in the code; at the time I didn’t have an emulator to inspect memory, much less a tool to disassemble ROM code). That skill is still useful to me nowadays to debug my own games!
Nowadays, we’d make the distinction between glitches (unintended consequences of code not tackling edge cases) and Easter eggs (cool stuff placed at places hard to reach by the designers, generally of cosmetic nature). Then Mew under the truck would be an Easter egg… if it wasn’t an actual Pokemon that could fight.