Women smile when you have eye contact with them

If you do not feel you are doing something wrong, then you probably are not

Looking at girls and having them smiling back is not a crime for sure

He's spanish ! and way of acting in Italy, Germany, France and Norway aren't the same for sure.
Especially talking about relations between men and women.
And I don't talk about africans or north-africans. Basic culture is different too.
I mean each culture has its proper / specail "codes" and for sure you need to be careful and first learn them, when arriving.
Same thing as for american / english way of saying hello ! - do you shake a woman's hand ? do you kiss her ? do you "hug" her - a few seconds - as in Norway ? (what is "normality" ? with Who ? When ? how ? in which circonstances ? what are social codes usually accepted ? )
This last point surprised me when I was in Norway and Sweden looking at people always hugging warmly during a few seconds. Because the "distance" in social relations is quite different depending on the country you are living in. And it can provide "strange situations", for sure.
i'm not used to hug as they are practising it. In France people are much more "distant", On their "reserve". Same thing as for crossing the look of a woman. Should be "light", not insisting. Same thing for staring at woman's body. Or, for ex. in Italy a wistle in the street, can be accepted if it's really a compliment not only a sexual "appreciation". It's not in France unless in south east, close to Italian culture.
I suppose if you do this in Norway - I never saw somebody who did it, in reality - people will be very surprised and desabrotating this kind of behaviour. I suppose...

They usually smile to be polite, Espacially if this is girls you have run into before, like in the grocery store or something. Also if you walk in the street and are having a good day, and you  are smiling, it is not unusual that norwegian girls smiles at you. Instead of starting a conversation, they sometimes smile, and then they go on with what they were up to. If you see a girl who smiles a lot to you and seems interested, then why not just go over to her and start a normal conversation. Then you will easily find out if she had some intensions or not.
I would say that norwegian girls in general are more shy the spanish girls. I have not met a lot of spanish girls, so I can only speak based on my experience with the girls I have met and talked to.