Sorry got cut off at the end!

The phrase “waiting in a line for lunch” refers to “the new arrival”, so we cannot separate those two phrases with anything. This has nothing to do with whether or not the phrase provides “extra information”. The rule (of good style — not necessarily grammar) is that we must always put modifiers next to the phrase that they modify.

The comma comes after “until” in this sentence because the phrase “waiting in a line for lunch” is technically extra information that isn’t needed. The writer gives setting details to help readers visually understand more if the context. This is called an interjection. If we were to remove the phrase, the sentence would read “Everyone is very peaceful, polite, and friendly until the new arrival is pushed aside by a man in a white coat…” The comma comes before “until” because the phrase “waiting in a line for lunch” does not directly apply to the rest of the sentence. I hope this helps!

This comma and the one following it are used to interject (squeeze in) information to the sentence. They can often be read like brackets and if you skip over the phrase between the two it should still make sense. I will record myself reading the sentence for you so you can hear how it would be said.

猛一看是插入语，压根就不是插入语，因为插入语是与原文无关的内容，或者至多某种解释，这儿显然是壮语，看，正在……时， 突然(♦suddenly ♦),，英语母语老外不会讲解语法，但是人家的母语，千方百计讲，都正确，你却不一定懂内部的东西。我的译文是严格按照原文结构翻译的，没有活译，但目的就是为了你正确理解。我现在研究或者遇到的反而都是最简单的问题。但以前是都是学习复杂的