A covered call by definition means you own 100 shares for every contract you sell. Even if you own some of that stock on margin you are not increasing your risk by selling the calls.
The parent was referring to OTM call selling, not covered calls only. Covered calls are pretty low-risk. Selling OTM calls includes selling puts, which is not low-risk unless you're unlevered (everything covered by cash.)
I don't see where you get the impression they were ever talking about selling uncovered calls. Selling out of the money calls has nothing to do with selling puts. As yes selling cash secured puts even with some leverage is considered very safe. Here is a fund that does just that.