Oh, poor little chap. I am on the spectrum myself, but this isn’t an issue I’ve experienced - also, I was diagnosed as an adult, so could clearly understand the care that I needed. Having said that... I always found the fingerpricking completely sensorily overwhelming, and would go weeks or months without testing because it was just too much. Luckily the Libre came to my rescue, and now I know what my levels are so I can dose correctly.
It could well be that he’s associating food with injections, perhaps try a low carb meal like an omelette that wouldn’t need a jab for - and tell him that it’s a meal he doesn’t need it for well in advance. He may accept the food then.