Dementia vs advanced cognitive impairment?

The first premise is not correct. At least at my brother's Assisted Living Facility there are many well into dementia who are not in Memory Care. They generally are not able to/or do not attempt to wander off facility, and they can generally come out of rooms to dining room when summoned for meals. But they would fail any dementia tests. One gentleman essentially just repeats and repeats the same story over and over 24/7, but walks about with his walker and doesn't stray far from his cottage. So I think facilities vary greatly. I would check with them as each case is absolutely unique. Safety is the main issue. Do check in and ask at several places. Some areas have organizations such as A Place for Mom who are paid by facility itself, who can tell you a lot about facilities before you even decide which to visit; they will question you and have forms and questionnaires for you that will tell them a lot about your elder, as well, the needs, the finances available and etc.

Usually the "secure" area of a facility is also the Memory Care. This is for people who are mobile and can wander away due to dementia, memory loss, AZ, etc. , and also for those who have shown signs of aggression. My StepFIL had Parkinsons/Lew Body and wasn't very mobile but he was 6'5" and made some threatening gestures towards staff so he was in the secured area for his own safety and that of others. This is in MN, so not sure if it is different in CA.

I think your friend is incorrect.