Review the item:
Because his glasses were so thick, Quincy refused to get
contacts,
he worried that equally thick contact lenses would make him look
like a bug-eyed space alien.
For a sentence to be fused, you must have two complete sentences run together with no punctuation. In the example above, a comma joins the two sentences. Because his glasses were so thick, Quincy refused to get contacts is one sentence. He worried … starts the second sentence.
Thus, the error is a comma splice.
To fix the problem above, you could put a period after contacts and begin he with a capital H.