Did you try during the "right" daytime? I think I didn't think of it first, too - but then remembered, that he's only in there during a few hours in the afternoon/evening.
You might need to talk with his brother (blue fox, whose name I can't remember anymore since I wasn't in the game for a couple of days now) afterwards or before again, in order to get there, too. I only remember that the daytime is important for this to start - and the next day in the morning you need to meet the Gorilla dude...
*spoiler content for innocent bystanders* if he’s talking to gen wouldn’t he be past the Bass/mac sequence? I would think he hasn’t gone to aeros shop to get what he needs for zorro (blue fox) to transform him hence why the questline is not progressing, if you have gone to aeros shop you need to talk to zorro, get the potion, drink it via your phone then sleep, that should let you progress then if you tell gen your ready to learn