I would say you are correct – the main contributor would be the tapioca. The biggest exporters of Casava root and starch are Thailand and Indonesia – both of whom have significant problems with soil contamination from heavy metals driven primarily by activities like mining, industry and agriculture. Cassava absorbs lead in particular at very high levels and a lot of that is down to agricultural land being either reclaimed from former mining sites in these regions or getting contaminated by run off from current mines.
I’d temper all that by saying as far as Consumer Reports go, they do seem to be the ones who shout the loudest usually about plant-based foods (and how dairy / meat is better) and most press stories you see on this route back to their content. Their trust pilot scores from subscribers is also literally flushed down the pan - so make of all of that what you will.