Hi Kath,
I suspect he may have been talking about Blight? Tomatoes and Potatoes are members of the same family and are attacked by Blight (apologies if I’m being patronising).
If that is what he was talking about then he is incorrect. Blight only survives on living tissue so it is quiet safe to put these plants on your compost pile.
It is, as Charles will no doubt confirm, a common misconception that you cannot/should not put blighted material on a compost pile.
Don.
