What an adorable little guy! While there are OCASSIONALLY Havs with coats that curly, it's not a typical Hav coat. No wonder he matted if he wasn't being groomed regularly!!!
He certainly could be a Hav mix. But he could also be a Bichon/Terrier mix. Both Havs and some terrier breeds have that color pattern. (obviously, Bichons don't, and I don't THINK poodles do either)
While there are waiting lists for good quality Havs from good breeders, unfortunately, there is also a steady flow of Havs from puppy mills, so they are not as uncommon as you might think. And puppy millers are well-known for cross breeding, either on purpose for "designer dogs", or just by accident because they aren't careful. (or don't care) We have several forum members who purchased puppy mill Havs, not knowing any better. they paid a lot of money for dogs who CLEARLY are not pure bred Havs. OTOH, they love them just as much anyway! One of these people coined the term "Half-anese" for her little guy!
You will probably never know exactly what he is... the DNA testing is not great at sorting out Havs from other small breeds, as there is a lot of overlap of genetic material in these breeds. I wouldn't bother with it! I think if you wanted to CALL him a Havanese cross, no one would question you at all. The shelters just guess... why shouldn't you?
One way or another, you are welcome here. As a small, non-shedding dog, he will be similar to our purebred guys in at least some ways... you may find, over time, that he is more like the other Havs than you think, or conversely, that maybe that's not what he is. Who knows? The most important thing is that he's adorable, sweet, and fitting into your family quickly and well!
We have a number of people here who have part bred Havs or not-Havs, and they are welcome members of our community too! You are to be commended for giving htis little guy a for-ever home, no matter WHAT his breeding is!