I can’t speak to who this person was or why they did this, but I did just want to mention that there is at least one good faith explanation that isn’t straight up bullying.
When I am in uncomfortable situations, I have a nervous chuckle. If I were in this call, giving this feedback to this person, I probably would have done that at least once. Thanks to some great feedback I once received, I learned that people were interpreting my nervous laughter as me thinking that what they were saying was dumb or wrong, even though this was not the case—I was just feeling anxious. It’s possible that this person really was chuckling at the OP to bully them, but it’s also equally possible that they were just feeling super nervous in an emotionally charged situation and laughed because of that.