Her suggestion is one that sticks with him. It means that his feelings, at least to some degree, are not one-sided. She wants to spend more time with him just like he wants to spend more time with her. She's just the one of the two of them brave enough to come out and say it directly instead of just creepily showing up at her favorite haunts in the hopes of yet another chance run in.

"Yeah?" he asks. "...you wanna finish our drinks and get out of here now and spend some time together?" he asks. It's not too late; he could take her to dinner, if she wanted, he thinks. Or back to the hotel. Or her place. Or they can just go for a walk; she knows the town and its offerings better than he does, but it doesn't really matter to Derek what they're doing if he gets to spend time with Lucy.

Which, again, is a huge red flag that he's getting in too deep, but he can't help himself. He likes her...a lot.