I love how lemon tek was your first example

In general I think people are referring to things that are either A) heavily proccesed and/or B) something that isn't naturally occurring. When they speak about "chemicals"

Your body is made to eat natually occuring plants and animals. Any deviation from that is risking long term issues. Effects that are very often (at least here in the states) ignored unless they just straight up kill you. And even then it'll probably take a couple decades before anyone actually does something about it. So, yes while many people misuse the word "chemical," their fear is not misplaced. You should be skeptical of things that are synthesized until they are proven to interact with the human body appropriately

Is light a chemical?

I think we need to understand what definition people are using for "chemicals". They usually are referring to highly processed ingredients, with highly processed preservatives, highly processed artificial flavors (called "natural flavors", but taken for example from the anal glans of a beaver... yes this is real and common). By the broadest definition, absolutely everything is a chemical. Generally, people should avoid any definition for a word that makes the word nonsensical. And also generally, you will find big lobbyist groups using that general definition to shell-game about the specific chemicals they are trying to protect.

When a food-concerned person mentions chemicals, they are referring to things like antibiotics or hormones, preservatives or processed sweeteners with known side-effects. Some of them are talking about isolates, like soy protein isolate to which there are valid health concerns.

And yes, sometimes people referring to chemicals don't know what chemicals they're complaining about. And yes, sometimes people complaining about chemicals are complaining that their meatless burger's consistency comes from methyl cellulose, (probably) completely harmless but absolutely artificial.

The same way some vegans are made ill by the thought of meat, some folks are made ill by flavor- or consistency-related facts in their food. I mean, I think vegans would be concerned to know the beaver anal secretions above was in some plant milks under the term "natural flavors".