> occasionally on the roughest roads some drips of molten iron fell off the back of carts while being transported
I agree.
When I studied ancient history (and Pompeii) in school we were taught that the 'ruts' were a feature of Roman roads, not a bug. Carts were specifically designed to have axle width match these ruts, and were consistent throughout the Empire [0]. I think this is a low quality article that misconstrues a research paper as actual fact.
I am going to Pompeii in September so I'll try and have a look at these iron patches anyway.