I think you have a beautiful tabby cat. If it were an Ocicat or Bengal, he most likely would not have ended up in a rescue situation. I think they're a little off on their age estimate, I would guess closer to 2-3 months old. My girls didn't reach 3 pounds until they were 3 months old.
Here's Charlee and Cali, first day home, 9 weeks old. To this day Charlee still looks surprised in most of her pictures.
You have an adorable Domestic Shorthair. Definitely not a Bengal or Ocicat.
We all go through a phase of wanting our moggies to be a certain breed, trust me! I spent years telling myself my gray cat was a Russian Blue (not with that cobby body!) and then a Chartreux (wrong color eyes, sigh). But no, she was just a very wonderful gray-blue Domestic Shorthair :}
When I got my black cat, my friend tried to convince me that she "just might" be a Bombay (no. Just no.)!
I know how awesome it would be to have a little gem in the rough in terms of having a "special" or certain breed of cat, but just think about how special your little guy is as himself, not as a certain breed. Also note that cats are never officially classified as "half Bengal" or a "Bengal crossbreed" or "part Bengal" - if a cat had one purebred Bengal parent and one purebred Siamese parent, the kitten would be a Domestic Shorthair - basically the cat version of mutt/mixed breed.
Also, I agree with Marie - no way your little guy is only 4-5 weeks old. Google "4 week old kitten" and compare - body structure doesn't match that of a kitten that young.