[Quote]...but always read the car scene as Jack being a bit distraught over the flashes he was receiving from his past. He just wasn't in the mood to go "weevil hunting".[End Quote]

Yep, that's how I interpreted that scene. Additionally, I interpreted Ianto's offer as being made simply because he could see Jack was distraught and distracted by what he believed he saw, and he didn't want Jack hunting alone while in such a state.