Doubt it was due to weather. Only known planes to divert due to the weather when trying to land a la MCO diversions to TPA/JAX/MIA/FLL. Inflight you would just plough on through rough air/bad weather.
Almost certainly a medical diversion I would imagine. Look at the map - St Johns / YYT is the first airport of any size when you first hit land after flying over the Atlantic. If you've got a very sick passenger on board, you want to get down a.s.a.p. to get them to a hospital.
If the weather is bad in MCO, you land somewhere near MCO so it's just a short flight when MCO re-opens. YYT - MCO must be a good 2hrs flying time.
Hope the passenger is making a recovery, if indeed it was a medical diversion.
I've been on a VS flight from orlando to manchester a few years ago (around 5) that was diverted to St John's because of a medical emergency.
This was in december. Due to it being a possible stroke, we descended rather rapidly to around 10,000 feet and then spent 45 mins in the worst possible weather I've ever flown in. We landed to find very strong winds that rocked the 747 for the 5 (yes, FIVE) hours were we are the apron whilst refueling. The larger refueling rig had frozen and they had to use a much smaller one.
We couldn't leave the plane, although spirits were high. Watching the snow through the windows was fun, although due to the wind, if felt more like we were on a boat!
We then took off into the same winter storm and landed in Manchester god knows how late.