Your answer really won't make a difference in your return. The 1099-MISC question "Was this work related to your main job?" is only asked to help determine if it was self-employment income. You were already reporting it as self-employment income (Schedule C).
"Related to your main job" can mean a lot of things. Was the work related to your professional training, previous employment, expected future employment, or was it your only source of income?
Basically the IRS is trying to find out if the 1099-MISC payment was for work that you typically do, as opposed to a one-time payment for something you hadn't done before and don't expect to do again.
