Great question — answering as the UphillTech team:
In the next episode, the couple in the scene you're referring to... turn out to be KGB agents. They're there to spy on Legasov. So her inquiry is most likely meant to see if he'll reveal the real reason for not wanting an upward-facing glass (that has likely been contaminated), or she's simply probing him with generic banter to see how he reacts and what all he says/reveals.
Full answer by GlenRunciter: https://movies.stackexchange.com/a/113089 (CC BY-SA 4.0).
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