Amen. I had a long and damaging relationship with somebody who did exactly what you describe. Used "boundaries" as an excuse for being a toxic human being, as many narcissists do.

A good test of the boundary-setter's true nature is whether or not they find alternative means of doing the thing or if they are just claiming "but muh boundaries!" to excuse their lack of being a decent human being.

If their "boundaries" prevent them from showing up at a funeral to provide a moment of comfort to the survivors of the deceased... well okay. There could be valid reasons. Suppose funerals tend to induce suicidal ideation in an individual. Certainly nobody would suggest that individual should risk a suicidal episode.

But, is the person finding an alternative way to show that care? Flowers, letters, a visit at some other time? Or are they just narcissisticly using it as an excuse to avoid spending time for the benefit of anybody other than themselves?