This statement is misleading and incorrect.
You are automatically signed up for Medicare Plan A (inpatient care) when you turn 65. You don't have to sign up for it. It is mandated. But it is also free. No premium is extracted from your Social Security check as it is for Plan B (outpatient care). You will not be denied your Social Security if you don't utilize Medicare Plan A.
I have Medicare Plan A because it was mandated when I turned age 65. But I don't use is because I am a military veteran and go the VA hospital for inpatient care.
I refused Medicare Plan B (outpatient care) because I get my outpatient care at the VA as well. That way they don't take $120 out of my SS check for something I done need or use.
Again the statement in the article is incorrect.
I think SeekAndFind is substantially correct. Yes, you get Medicare Part A automaticity - and for free - when you turn 65.
But suppose you then, for whatever reason, refuse it. You write Medicare and tell them to take you off their Part A enrollee list. In that case, you would lose your social security benefits! Weird, huh?