That's an extremely adorable picture but not really the best one to see much of the cat. We can see he has cute spots on his belly (which is common in many tabby cats.)
I can't totally see the arrangement of spots on his sides. .. but looks like it MIGHT be more arranged in broken vertical stripes rather than the more random pattern that is more common in the Egyptian Mau.
He truly is probably not an Egyptian Mau , but a very handsome Brown Spotted Tabby Domestic Shorthair --- which would not make him any less special. and I'm sure you agree!
It would be extremely unlikely to find an Egyptian Mau kitten at a shelter. Even finding an adult Mau in a shelter would be quite uncommon... But the odds are even more against a 3 or 4 month old kitten ending up at a shelter
A breeder is certainly not likely to dump a young kitten (And even if it's a breeder who is just in it for money, why would they dump a kitten instead of selling him?), and someone who just spent at least $600 for the kitten is not likely to turn around in a month or so and leave him at a shelter or dump him on the street. Most 4 month old EMs are not going to be outside unless on leash or in a very secure outdoor cat enclosure. So to have been a stray, he'd have to have somehow have escaped and got lost soon after going to a new home ( or got lost from the breeder's home) and then was never found. & usually one of the first steps would be to check shelters. And apparently he had no microchip.
I often use the comparison that an Egyptian Mau is much more rare than a hairless Sphynx . And how many Sphynx kittens are there running around as strays or in shelters? At least I sure don't see many! In fact I have never seen one. I've seen a few adult Sphynx pictured on shelter websites. but not kittens. And surely the numbers of lost / abandoned Egyptian Mau kitttens must be much much lower.
But sometimes cats can resemble a breed without actually being related. especially when it's not a super extreme looking breed .
Like the vast majority of cats, he's probably mostly from ancestors who came from the same part of the world where he was found. . ( Of course, if you got him in Egypt, then he could be considered like a "native Mau". )