That quote is taken out of context. The wider discussion on the wiki page suggests that Bruno's scientific views as well as his philosophical ones were responsible for his conviction, including:

"claiming the existence of a plurality of worlds and their eternity;"

Bruno has been described as a "walking, talking shitstorm" disliked by Galileo and Kepler, but he was a free thinker who infuriated the church with his recalcitrance and iconoclasm. Saint Carol and his bank of merry men still thinks he was a heretic to this day.