Yabu, sorry - it's not a great way to handle a toddler. Laughing, especially, smacks of contempt.
I would get involved if a parent walked away. I would stand and talk to the child.
Sorry but you did ask - if a child is having a tantrum, don't leave them. Stay there. Wait till they stop. Don't look at other people, concentrate on your child. Just be calm and wait, don't make a show of 'winning' or having the upper hand.
People don't want to see that, they want to see it resolved and someone being a patient and calm parent, not a battle of wills.
What you are doing currently would look worse, to me, than what the toddler is doing. You have to accept that they feel bad, that they are little and don't know how to manag their emotions.
Btw I often found ds1 was hungry or tired when he behaved like that, and an offer of a snack, often sorted it out.
I hate seeing parents laugh at their crying children.