No it's a stupid poem meant to deceive. Valid "matter" for the Eucharist is bread made from wheat flour and water and nothing else. By adding, "HALF AN OUNCE OF ARSENIC", as the tale suggests, would invalidate the matter and no Consecration would take place and every faithful Roman Catholic priest would know this. The author of this "tale" has a tail of his own, and hooves.
And even if it were valid matter, the substance change to the Body and Blood of Christ would still adhere to the accidents of poison bread.
So this demonstrates nothing except ignorance. No two ways about it.
SD