The evidence is that there is a small correlation between having the therapy and having a stroke. It’s not clear how common this is as the studies done do not agree nor are they robust and conclusive. Nor does a correlation – which simply means that the two things appear together slightly more than chance would predict – mean that one causes the other. If you want to consider that this type of therapy causes stroke, you also have to consider that imminent stroke causes neck pain and the sufferer seeks help for it. Which is as likely as the other and that there is no link at all. More good quality studies are needed. Who knows what the current body of evidence means, certainly not anyone who has done a study into it.
Case studies and anecdotal evidence are the worst sort of evidence. The best (and even this is never foolproof) is a systematic review carried out by an expert body such as a Cochrane review.
So if you have neck pain and wish to have chiropractic therapy on it, I suggest that you read about the very slight risk and make an informed decision