You know, it's funny - I had an incident with a student hugging others at lunch just last week!
I'm 100% sure he thought he was just being friendly. But the first little girl did NOT want to be hugged. He was rough about it, standing up and squeezing her head hard against his chest, and it hurt her. Additionally, he didn't put down his spoon first and he got yogurt in her hair.
My TA and I intervened. She got the girl cleaned up and I spoke to the boy about appropriate lunchtime behaviour. I also warned him that if he couldn't follow the lunchroom rules, he would have to eat alone.
He left the girl alone after that, but starting hugging a little boy soon after. He had a runny nose at this point and wiped it on that boy's neck, getting snot on him. The second boy was horrified and started to cry.
So we had to move the hugger. He had been warned of that consequence and the other children were now upset and not eating,
This isn't your son, OP. We talked with the parents that afternoon and explained our rational, which I wish your school staff had done with you. But there as really not a lot else we could have done there to ensure that everyone got a safe and happy lunchtime. We don't have enough staff on duty to lose an adult to a permanent seat at one table to supervise.