A gastropod shell is largely calcium carbonate, secreted by the mantle at the shell margin. An animal that reaches fifteen to twenty centimetres of shell length needs a correspondingly large calcium budget, and leaf tissue is a poor source of it. Where soils are calcium-poor, the snail's rasping radula finds better mineral in stucco, lime render, mortar and painted plaster.
The behaviour is well documented in introduced populations in Florida and the Caribbean, where reports of snails abrading house walls accompany the crop damage. It is the same feeding apparatus at work: a ribbon of chitinous teeth drawn across a surface, removing a thin layer with each stroke.
What is often overstated is the scale. Individual snails remove very little material, and structural harm requires a heavy, sustained infestation. The more consequential problem is agricultural, and the species is also a host for the rat lungworm parasite, which is why control programmes take it seriously rather than treating it as a curiosity.