Hold the chumus, please

There's a kerfuffle brewing in Israel between Rav Ovadya Yosef and Rav Mordechai Eliyahu over the status of roasted sesame seeds, whose byproduct-tehina sauce-is used in the production chumus, arguably Israel's national food. Apparently, when sesame seeds used to make the tehina paste for hummus are roasted and shelled by non-Jews, the resulting hummus is not kosher, according to R' Eliyahu. His aide, Rav David Lahiani, said that when non-Jews are involved in the cooking process of foods, this causes them to be designated non-kosher according to Jewish law.

But bishul akum is kosher, so long as it's under a reliable hashgacha, isn't it? I think that either the article is incorrect or there's something wrong with the psak.

Anyone have any ideas?