It's definitely an error by the company. Box 3 is gray because it's not supposed to be used. I wonder how the company filed it with the IRS. The IRS is not going to accept it with box 1 blank and an amount in box 3.
Putting the amount in box 1 is the right thing to do. And it's self-employment income. You will have to pay self-employment tax if your net self-employment income is over $432.
