I honestly don't know without imaging and a read of the images by a competent authority, which I am not. It is plausible that there could be 'some' fibrosis inside the aorta, just as there is often 'some' fibrosis in aging hearts' chambers' endothelium. But my money, if I were to put any down, would be on plaque if there is any measurable occlusion because the fibrosis would have a very small 'footprint' in any images where scales could be used. It's like the difference between a sheet of paper and the entire pad, except the 'entire pad' would be plaque. Fibrosis is another name for scaring, whereas sclerotic tissue is more substantial in thickness. Also, the lesions and subsequent scarring that is left behind by the ablation procedure is only normally located in specific areas, usually around the pulmonary veins. The fibrosis from aging and arrhythmia, and from a defective mitral valve, would be much more widespread if added up in total area. This is my inexpert understanding.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9557071/#:~:text=Myocardial%20fibrosis%2C%20resulting%20from%20the%20disturbance%20of%20extracellular,arrhythmia%2C%20heart%20failure%2C%20or%20even%20sudden%20cardiac%20death.