The cause(s) of lupus are still unknown. There is a difference between the underlying causes (a set of genes for instance) and the triggers (environmental insults, meds, other diseases, physical injuries, or stress). Stress plays some kind of a role but for someone to say that stress "caused" your lupus.....I don't think there is any scientific evidence to support such a statement. Check out this link for a good discussion of the subject.
Just the subject of triggers is a difficult and much debated subject. I suggest you read the book "The Autoimmune Epidemic" which gives a good overview of AI diseases and some clues as to what might be causing an increase in them in modern life. You can buy it on Amazon.com.
One thing that is for certain....most people are ignorant about auto immune diseases like lupus. I was before I got sick 5 years ago and would be happy to be ignorant of them again.