Does Vorpal Spikes proc Rylai's crystal scepter slow?

Some people say it does, and some people say it doesn't.

My friend is pretty sure Cho'Gath's Vorpal Spikes does proc Rylai's Crystal Scepter's passive, but we both can't test at the moment. I thought it didn't proc on toggle skills, but he swears it does. The people in the threads I mentioned seem to classify Vorpal Spikes as an AoE spell rather than an on-hit toggle skill... Anyone have some insight on this?