He is a man with strong, passionate and sincerely held beliefs. In my view Pastor McConnell's mindset was that he was preaching to the converted in the form of his own congregation and like-minded people who were listening to his service rather than preaching to the worldwide internet.
His passion and enthusiasm for his subject caused him to, so to speak, 'lose the run of himself'."He added that "the right to freedom of expression includes the right to say things or express opinions that offend, shock or disturb..."
UPDATE: Here is the full text of the opinion in DPP v. McConnell. Law & Religion UK has additional discussion of the decision.