Yes, they are not real apples, different genus, tropical fruits, very watery, hundreds of different hybrids, varieties of shape, color and taste, very yummy and juicy, some will have sour and bitter taste.
Have tried to grow different varieties and at the end I stick to this one, the sweetest ones, they tastes sweet even when they are young. I check with google, the latin name is "Syzygium aqueum", but its better if you try the key word "jambu air" in google picture search, you will love what you see..
