Only speaking from my similar experience, I would agree with this child’s mother, especially if he is on track with everything else. He sounds completely fine to me. My daughter was only 17 months when we went to Australia but the experience was terrifying for her, she understood that she was far away from home. She knew the language, the people, the climate, the food - she understood that she wasn’t home and nothing made sense to her,.
She was always crying as soon as one would make a loud sound from having fun playing and the only people she would take to was grown-ups because they were less daunting to have to deal with. They treated her how she was used to being treated, gently and patiently.
When she met them (her cousins) for the first time, my nieces were very loud and typical “kids” not much older than her, my DD was very frightened of them and was at that time very shy and quiet, not very active. My nieces kept playing rough with her or kept wanting to play with her but she didn’t want to because she was scared.
French kids on the other hand, I wonder if they are even allowed to talk or act like kids, they all seem so quiet and reserved, strictly disciplined, strangely well mannered for kids and play quietly in the park - this is all what my daughter knew for 17 months. I noticed the big cultural differences when I was in Australia, Oh how I miss watching kids be just that, kids!
It took my daughter some time to finally realize that that’s how kids are there, more outgoing and loud. Since our return to France, my DD is like the foreigner, she became just like her cousins. Everybody noticed how different she became upon her return.
Unless you’ve been in that situation before, it’s not easy to put yourself in someone else’s shoes, actually I believe that’s impossible. It’s just as daunting for a 2 year old as it would be for a 50 year old. Kids need familiarity to feel safe. People assume what life must be like for me as a foreigner but I don’t bother to argue with them about how wrong they are - it’s not the same seeing a Country as a tourist.
My daughter’s daycare question my parenting all the time, I just say, sorry I’m not French and move on. Theses are people who have never left their own Country, let alone have had experience dealing with a foreign parent or child. There are some things my daughter isn’t doing that a typical French child her age should be doing but in Australia, these are things kids her age aren’t meant to be doing so I’m never concerned. I keep trying to explain cultural differences but that just goes through one ear and out another.
I hope my ramble helps a little