In 2007, Richard tells Sun that he watched Kate, Jack and Hurley die. At the Swan in 1977 there is no reason to believe from what we saw that Richard is there while the Incident is happening. If Juliet detonated the bomb, it would seem that they all died then and there.
This just makes me think even more that the bomb had nothing to do with the white flash. Of course, it doesn't shed any light on the deaths that Richard claims to have witnessed.