I think it can be synonymous given the context. A virus can essentially "kill" a computer can't it? Just like poison kills a person? I was going to make a quip about worms in the apple, but don't think that necessarily works from what I know about worms (although admittedly I don't know much about worms).
A virus is a pathogen which infects organisms and starts replicating. Since it doesn't belong in the organism and can cause potential harm to it; the organisms immune system will try and fight it off and it's in fact because of the Immune system working overtime that we initially get sick.
A poison or as it were in this specific case; a toxin is usually a small molecule which will cause what might be called a chemical reaction when it comes in contact with biological tissue. The severeness and scale of this reaction is what may or may not kill you
Biological nerdiness aside; it's just a silly argument about word-play and analagies so lets drop it, but I hope you learned something : )