I'm not sure I would categorize that as "stigma": that sound more like fear - fear of how to deal with the person, fear of saying the wrong thing, fear of being embarrassed. And that happens. A lot.
Stigma (at least as it is defined by the dictionary) involves judgement (in the eye of the beholder) and shame on the part of the stigmatized. It's all about disgrace. And while the way some people treat people with dementia and their carers IS disgraceful, that's more to do with their shortcomings. While I've come across the whole gamut of embarrassment and the rest of it, I've never encountered the "you have this, it's your fault" that stigma implies. I'm not saying it doesn't exist, but I've not seen it.
Watch the video
'shifting the perception of Alzheimer's disease and creating positive outcomes' on Youtube by Kim Warchol