They are merely "obsessed."
Original NWT reads: "If any man teaches other doctrine and does not assent to healthful words, those of our Lord Jesus Christ, nor to the teaching that accords with godly devotion, he is puffed up [with pride], not understanding anything, but being mentally diseased over questionings and debates about words. From these things spring envy, strife, abusive speeches, wicked suspicions..."
2013 Revision reads: " If any man teaches another doctrine and does not agree with the wholesome instruction, which is from our Lord Jesus Christ, nor with the teaching that is in harmony with godly devotion, he is puffed up with pride and does not understand anything. He is obsessed with arguments and debates about words. These things give rise to envy, strife, slander, wicked suspicions..."
Now, however, they are also officially "puffed up with pride," instead of possibly being "puffed up [with pride]".