The difference is that the company that contracted you isn't managing your day-to-day work.

Company hires you and says "we need a website that does X" and leaves you to do it. You might be a contractor/free-lancer.

Company hires you and says "we need a website that does X, you need to work in the office and/or use our hardware, and we want it written in React, and you'll be working closely with JimBob the Manager." You are probably not a contractor/freelancer.

Yes, there's some grey area in there. It's a combination of the three factors in the ABC test that determines employee vs contractor.