Two crazy bugs back to back...

[Artifex1]

The first one is I had ampitheaters in my first 4 settled cities and took legalism and it only gave me opera houses in my first THREE cities.

The second one on the next turn..Montezuma said I broke my promise to stop expanding near him and I DIDN'T DO ANYTHING. I haven't founded any cities nor bought land...

??

 

[Browd]

Double check your fourth city. Are there any culture buildings that are labeled (FREE)?

On the other bug, I've gotten this on occasion from normal (passive) culture border expansion. May be a bug, but who knows.

 

[krc]

The first one is I had ampitheaters in my first 4 settled cities and took legalism and it only gave me opera houses in my first THREE cities.

Did you have a puppet city that you captured before settling your fourth city? If you did, then it got the extra culture building....

 

[Browd]

Oh, yeah, this just got tested and reverified earlier this week in another thread. A puppet conquered after you take Legalism doesn't get a free culture building, but a puppet before you take Legalism will.

 

[Karatekid5]

The second one on the next turn..Montezuma said I broke my promise to stop expanding near him and I DIDN'T DO ANYTHING. I haven't founded any cities nor bought land...

I've had similar situations like this happen before. I was spreading my religion around to Sejong's cities with a great prophet, and when I converted his capital he told me to stop. So, I moved the great prophet to another civ. However, a few turns later, my religion spread naturally to one of his other cities, causing the promise to instantly break, Sejong to denounce me, and it ended up starting a 300-year war between me and him.

What probably happened was that one of your city borders naturally grew and chose a tile near Montezuma's territory.