BobKamman is absolutely correct. I should have made it clear that this referral income was not related to any ongoing activity, but rather something that just happened to fall in the lap of the taxpayer by chance.

Of course, had this happened to be a single successful outcome of an activity that the taxpayer was considering as an a trade or business, but without prior or subsequent success, the income should probably be reported on schedule C and be subject to SE tax.

My bad. This is my initiation  into this forum. I'll do better next time.