A statement like:
"It lies 168,000 light years (987 quadrillion miles) away
is highly misleading in the framework of Special Relativity: There is no universally agreed upon "at the (same) time" in Special Relativity for distant events.
It is just as valid to say that the explosion took place at the same time the car was invented. It is just a question of the observer's frame of reference (that's why it is called "Relativity").
The only thing that is non negotiable here is that there is a causal link between the space-time event of the nova explosion and the the space-time event of the arrival of the light emitted during the explosion on earth. There is no observer that can break this causality. But there is even a frame of reference that puts these two events at the same spot in space and time!
For the more mathematically minded: Time and space distances depend on the observer. What is fixed is the space-time distance D, namely:
D = sqrt( (x2-x1)^2 + (y2-y1)^2 + (z2-z1)^2 -c^2*(t2-t1)^2 )
which happens to be zero for causally linked events.