Weird or is this normal neighbor activity?

My(38M) wife(35F) and I have two places. She(my wife) has an apartment, and I have my house. Unusual situation but we both need space sometimes so we have two places. We stay together 95% of the time. That’s not what this post is about though. Today her downstairs neighbor (50’s M) started entering the code to the apartment door. My wife, her son (5m), and I are all home. It’s obvious we are all here as both our cars are out front, and we all walked in together past their first floor apartment. My stepson and I are playing with monster trucks and ramps I built. We hear the door beeping for electric code lock, and I go to open the door as my wife’s sister likes to randomly stop by. The sister has the code but I was going to open it to make it quicker. When I open the door the downstairs neighbor is standing there and he had valentines candy for our son with him. He said “oh is the little guy here?” I moved out of the way and signaled our son to go grab the candy. He leaves and I shut the door. It took a minute to register, but is it weird that he was going to enter the code and just let himself in? As far as I know he doesn’t know the code and his wife (50s F) only had a key while we were on vacation recently to feed my wife’s cat while we were gone. So what are people’s thoughts on this? My wife said “that was weird, he doesn’t know the code”. And I decided to post here before I speak to anyone else about this. In my head I’m thinking “WITAF was he thinking? Why not knock?” I’m not here all the time as my wife likes to kick me out when we fight and have me stay at my house that’s about 15 miles away.