Actually the term “Resident Alien” is not used. The term that is used is “Legal Resident”
Perhaps you are right:
https://www.uscis.gov/tools/glossary/permanent-resident-alien
Permanent RESIDENT ALIEN
An alien admitted to the United States as a lawful permanent resident. Permanent residents are also commonly referred to as immigrants; however, the Immigration and Nationality Act (INA) broadly defines an immigrant as any alien in the United States, except one legally admitted under specific nonimmigrant categories (INA section 101(a)(15)). An illegal alien who entered the United States without inspection, for example, would be strictly defined as an immigrant under the INA but is not a permanent RESIDENT ALIEN. Lawful permanent residents are legally accorded the privilege of residing permanently in the United States. They may be issued immigrant visas by the Department of State overseas or adjusted to permanent resident status by U.S. Citizenship and Immigration Services in the United States.