One way to tell would be do you have first hand knowledge about manufacturing process? Could you make this? The casting process is straight forward or maybe it is not. If the original model is investment cast there will not be any parting lines. There can be random flashing if cracks form in the mold/flask during burnout to remove the wax. Two part sand molds will leave parting lines and porosity and if the pieces are finished in a hurry you will see them. But, if you take the time to go over the piece, those lines can be removed and porosity can be filled or burnished.
Fabrication by forging; you start with a solid disc then you have to sculpt the metal by physically cutting away the areas you don't want to reveal the design. This makes me think about the tools. What tools were on the bench and would one have the means to produce the design using those specific tools. But, the grain in forged iron will only be visible if the patina is not present and then only after an acid etch.
Long story short, IMHO, one would need to have knowledge about how it was made to say what it is, cast or forged. Or as Dale put it the concrete floor on a cold day will reveal the truth 🫢.