Generally speaking, British courts, when making judgments on constitutional matters regard themselves as interpreting existing law, rather than creating new law.
But technically speaking, any legal precedent established by a court can be interpreted as "creation of new law".
For the avoidance of doubt, the sources of law in the law of England and Wales include: statute law, constitutional convention, prerogative powers, common law, and legal commentary. I may have missed some out and may edit those in later.
Common law refers to the judgments of courts. So here we come to your question:
Several legal principles and precedents were established by this judgment, and you may consider this new "law":
The court held that prerogative powers are justiciable - courts can limit the scope of these powers
The prerogative power in question had limits. It can be limited when its use has an extreme detrimental effect on the democracy of the UK and parliamentary sovereignty.
What is important with point one is that the court recognised that this power has always existed, stemming as far back as the bill of rights in the 17th century. As such, the court is implying that it is creating nothing new, but recognising a law that has always existed. You will see a LOT of this when studying constitutional law.