That means London bridge in London is the real one?

The London Bridge in Lake Havasu is the one from London that was removed to build a more modern one. The bridge in Lake Havasu was purchased by the property developer and rebuilt there as a tourist attraction.

The London bridge in Lake Havasu is the original London bridge, they tore it down and brought it over so they could build a modern bridge over there.

This bridge was disassembled in London, UK. And then sent to Lake Havasu and rebuilt.

Above answers are correct

This was the London Bridge is Falling down my fair lady .