Was it a radioactive Dragon fruit? Maybe you'll get super powers like uhh the ability to grow a few feet in a few months and you'll develop a very bland sense of humor.
LOL, hilarious... I'm sure the dragonfruit feel burned! I'd be careful, they may rise up in your sleep and take you out. I don't think I'd want to make them angry, especially not the heavy ones!
As for the OP, it's possible that the thorn had some dirt on it. Getting a deep wound that is contaminated in some way, including an almost microscopic piece of thorn still stuck in there, would react this way with any healthy immune system. It should get slightly hot, swollen, and red for a few days. The cause for concern is if the swelling is out of control, or seems to be spreading or affecting your breathing, or doesn't appear to be healing after two weeks. If it's just localized, it's totally normal. I find that a jeweler's magnifying glass and a needle are really helpful for finding pieces of debris you can't see with the naked eye. Antibiotic ointment applied liberally with a bandaid and massaged a little from time to time will help your skin work out whatever is still stuck in there that's causing the reaction. An allergy would be more pronounced, like the entire hand would swell up to nearly twice its size and be very painful. The wound being swollen is normal, that's what wounds are supposed to be like when the immune system sends little fighters in to defend the area. I am constantly covered in wounds and scratches... it is a hazard of the hobby, especially when you work outdoors and deal with a lot of mature plants with very sharp edges!