I don't understand why people call this free money. It's not. It's part of your total compensation.
People don't say "hey employer provided health insurance...yes! Free money!" When usually that is a more lucrative benefit than the 401k match.
I hate semantic arguments online, but you at least understand why people view it that way, right?
You get your salary regardless of what you do with your money. Nothing more is guaranteed.
However, if you just move some of that salary from one place to another under a specified set of circumstances, you get more. So, call it what you will. It's not guaranteed, and the criteria to obtain it do not include a material cost, so "free" is close enough.
Most of us pay something toward our employer-sponsored health insurance and we never see the part they pay, so people are less likely to view it in the same way.