"I'm having coffee with them at work."
Probably because the first time round when you get to this it is too early in this course.
In terms of 'correct' Chinese I would think 跟 is better, but it should be an alternative correct answer, leaving 和 in the main answer to cater for people who maybe aren't so confident yet in their Mandarin.
公 (gōng) = public/collectively owned
司 (sī) = to take charge of/to manage/department
公司 (gōngsī) = a company/firm
In a previous lesson we saw:
办 (bàn) = to do/to manage/to handle
公 (gōng) = public/collectively owned/common
室 (shì) = room/work unit/grave
办公室 (bàngōngshì) = office/business premises