Of note, that article was mostly highlighting older motorcycles as dramatically worse when comparing them to newer vehicles.

See this article to show how a modern motorcycle would be ~100x less polluting than the example vehicle given in the article referenced:

https://www.acem.eu/new-euro-5-environmental-standard-for-mo...

Does that include motorcycles that have illegal aftermarket exhaust systems with all emission controls removed in an effort to make them as loud as possible? This accounts for about 80% of them, so it's irrelevant how they function by design.