Yup it's his save / Mew as mentioned. You can only see / download when logged in and registered so i've shared / mirrored the save else where in the hope's it will be around for years to come.
That's my plan, the Mew is already on my 3DS copy of Pokemon red. I hope i'll be able to transfer it over to Moon / Sun along with all my other GEN1 Pokemon I caught 16 years ago.
Indeed that's what I had done many years ago on my Yellow save, it's the same end result as going through Pokemon stadium which has been the only way to ever get a surfing Pikachu outside Japan for GEN1. So we have the only western GEN1 event Pokemon archived, however GEN1 in Japan had a few more event Pokemon in addition to Mew, including a flying Pikachu:
Nintendo 64 Pikachu - This Surfing Pikachu was distributed to 10,000 players by presenting a lottery ticket obtained from purchasing a Nintendo 64.
CoroCoro Pikachu (Surfing and Flying) - This Surfing Pikachu promotion was revealed in the October issue of CoroCoro Comics, and the later Flying Pikachu promotion was revealed in the November issue. However, there were only 20 Pikachu available at each promotion.
University Magikarp - This Magikarp with the special move Dragon Rage was available for 20 players through the "Tamamushi University Hyper Test" campaign in magazines published by Shogakukan, along with the rare Magikarp card, which is based on this Pokémon.
Pokémon Stamp Pokémon - Two Pokémon, Fearow and Rapidash, with the special move Pay Day were available through the Pokémon Stamp campaign that ran in various magazines published by Shogakukan.
I'd say the chances of any of those event Pokemon ever making their way online and then to an English speaking website such as Project Pokemon are almost none, especially the University Magikarp and Flying Pikachu. Never say never though.