It’s probably good that you’re confused… the alternative would be that you’re apathetic and not really paying attention to what you’re reading. People are literally using/misusing these terms to mean different things.
Soul ties can form with anyone through intense experiences. Sexual connections, trauma bonds, deep friendships, even family relationships. Most spiritual communities recognize that you can have multiple soul ties throughout your life, and they can be either healthy (supportive friendships, loving partnerships, like a soulmate) or unhealthy (draining, codependent, manipulative, like a karmic).
Twin flames are understood differently. You have only one twin flame. Your literal mirror soul. The connection is permanent and unbreakable, designed to trigger deep shadow work and spiritual evolution. Some teachers say twin flames have their own unique “soul tie” or energy cord that’s fundamentally different from regular soul ties because it’s an organic part of both souls rather than something that forms through experience.
Personally, I do think this is probably terminology that doesn’t really add anything of value. Some will consider twin flames a soul tie, others won’t because they’re somehow different. It doesn’t really matter.