He most certainly is. He states, and rightly so, that these men are impounded and have no authority, even if they remain the visible head of the Church, due to manifest heresy.
No authority? Here's one of the paragraphs from what Fr. Chazal says on the backcover of his book, Contra Cekadam:
Quote:
"It will not hurt sedevacantists to hear that if something is left of the authority of Francis, it is in no way to enable him to spread heresy any further. Barriers against heresy were erected by our Fathers: let us use them even against a reigning Pope." end quote.