All freeways and interstaes are highways, not all highways are freeways or interstates.
That’s just the definition. Usage varies by region and personal background. In Connecticut, where I grew up, the common description for the Interstate is “Highway”.
Per Co-Pilot AI:
The official name of the U.S. Interstate system is the Dwight D. Eisenhower National System of Interstate and Defense Highways. It’s often simply referred to as the Interstate Highway System or Interstate System. Named after President Dwight D. Eisenhower, who championed its creation, the system was designed to facilitate efficient transportation across the United States and provide critical infrastructure for national defense.
So, while the term Interstate is more specific, “highway” is completely accurate.
It seems like any and every road is a highway.