Meow it sounds like your son was very much medically at risk. There is a link between anorexia and ASD. With an eating disorder though, force feeding is a last option and used when the person is medically at risk (as it sounds your son was). I'm not sure how you force fed and I truly do not hold any judgement, I have seen many families at this point and grew up with a brother who had a VERY restricted diet and my mum tried force feeding (it didn't work). The way I would go about it (and many may consider this force feed but I personally don't) is gradual exposure. Therefore choosing one food, then choosing a reward (eg a fav food he only gets in relation to 'trying new food', a special toy, etc). First the goal would be (if his reaction is to even not go near new foods or accept them on his plate) is have the new food on his plate, then touch, then smell, then touch his lip, lick and so on. I would keep a chart and he can put a picture or photo of the new food up when he has actually tried it and get a really big reward.
Overall, any feeding program should be under the guidance of a doctor to ensure the child is medically healthy. I have seen children go a very long time without food and drink just to avoid eating a new food and so medical guidance is important. Children with ASD are likely to go a lot further than another child and defy the 'they will eat when they are hungry' rule. With that said, I have recommended that approach before when a child was only accepting a few foods.
I guess what I'm trying to say (and I don't think it is coming across very well so I do apologise) is that every child will be different and it is not always easy to make the right choice. Meow, for your son it sounds like the idea of a new food was the problem (I may be wrong, what do you think?) and in this case I can see where forced feeding could work, however; if it is a texture issue I'm not sure it would (Tony Attwood has some info on this).