How did squid become calimari?
It was calimari first, that word goes back to the 16th century. Squid only goes back to the 17th century.
The same way that the conch sea snails turned into scunizzi.
Other languages have other words! The seafood culture of the Italian peninnsula predated the U.S. by many centuries. Calamari is the Italian word for a specific kind of squid. One of the roots in the word is "mar", which means "sea."
Fresh calamari, before slicing and cooking: