Because he has spent an academic lifetime studying that question, and recognizing the unique obstinacy of that word, in that you cannot pre-commit to define it despite some intuitive consensus on what it may mean. https://iep.utm.edu/hard-con/
If he thinks GPT-3 is a simple consciousness then any language model would be a simple consciousness. That doesn't make intuitive sense.
Maybe language itself is an attribute of conciousness? Means, the image of self and the image of the environment, must some how reflect back, and this reflexion is expressed by .. language? Be it, sound , gestures, visual, chemical.