I might've just gotten lucky. But I just kept going in and out of the store (going for a walk between, because you can't immediately go in) and buying one thing every time I go in. Eventually I checked the dialogue with the bot and other than "small talk", something along the lines of "talk about going outside" came up and I clicked that. For me it triggered like a week (in game, of course) after I started trying to get it to trigger, maybe a bit longer.