Ask him if he enjoyed Deadpool. His reaction will tell you everything - you don't need to sit him down and lecture him, just casually ask. If it's meant to be a secret, if he's hiding something, he'll want to know how you found out. If it's not, he'll answer you and presume he mentioned it at some point.
Regardless, you know that your husband is talking to someone local who has shared a great deal of knowledge about things like taxi costs and restaurant menus. You know that he is not telling you everything. You know that he's happier than usual.
Don't lie to yourself saying he's too busy, or Deadpool is a man's film, or it's too new to know anyone here yet. He does. Whether innocently or not, he knows people and has time to talk to them, because he knows local information. He has people to go out with until midnight when you're not around.
It's totally okay to decide to approach this in your own time, or to not approach it all, if that's what you want to do. But lying to yourself will drive you mad. It stops you sleeping, it stops the pieces fitting, because you're desperately convincing yourself that things fit when your brain knows that they don't.
It's a bit weird, regardless, to go to the cinema on your own and then keep it a secret. Most people would mention the film, or that they'd been, it would just come up in day-to-day conversation. It's more weird to not mention it if you're asked what you did that day. He mentioned going into town so you knew he wasn't working... so why not mention the cinema? For some reason, he doesn't want you to know. That could be that he's taken someone that he doesn't want you to know about or thinks you wouldn't approve of, or that he took one of the kids when they were supposed to be at school, or that he has another reason for going alone - a friend used to go to the cinema to cry so nobody would see her, for example, although it's unlikely to be that if he seems happier in general. He could even just have taken a new colleague to start a friendship, although again, I'd wonder why he hadn't mentioned it if you're not the jealous type.