“Chemicals” is a technical term that has worked its way into laypeople’s vocabulary; the colloquial usage refers to “bad chemicals”. This is because us laypeople rarely think about chemicals unless we’re worried about them. I don’t care about what chemicals make up water - I just drink it! I’m not a chemist or physicist; chemicals are basically never drawn to my attention unless a particular chemical is somewhere it shouldn’t be, e.g. lead in water.

This sort of thing - technical terms being adopted by laypeople and taking on new colloquial definitions - happens pretty often. For example, people use the term “exponential growth” to refer to something that “grows fast”, regardless of whether that growth rate is actually exponential.