Any other explanations as to what's causing this BTC upsurge?
We can't actually pinpoint what's the
"exact" reason behind the current strong demand that leads to a price increase. There are lots honestly that we can consider as reasonable factors.
You can refer to some crypto news portal around and take those recent news as reference. Don't want to link some as it was easy to search. From there, you can speculate what could be the reason for this price increase movement.