I don't think there is any known association with exertion, but it's impossible to rule out. Pre-eclampsia is mind-bogglingly complicated, and new information is emerging all the time. For example, it is coming to be understood that the patho-physiology of pre-eclampsia from early pregnancy is different from late onset.
What I would say is that we know that, over all, keeping active in pregnancy is beneficial. The benefits of continuing exercise hugely outweigh the risks for 99% of women. No one who is pregnant should be deterred from continuing exercise by this tragedy.