Am I the only one that thinks it's weird to call a weed killer a pesticide?

Herbicides are a pesticide [1]. (Alongside insecticides, fungicides and fumigants, among others.)

[1] https://www.epa.gov/sites/default/files/2017-01/documents/pe...

Technically, yes, but it's a similar relationship of humans being animals. If you say animals, the audience will assume you're not talking about humans.

Scientific terminology should be precise, not based on colloquial usages

Did you mean "beast" or "creature"?