B12 is a bacteria, which isn’t necessarily found within either plant based or animal based food. That scholarly source article only gave an example in the abstract of algae that has traces of b12. Meat generally isn’t healthy for you , an example of this is the WHO who have classified that it’s a carcinogen matched with the likes of cigarettes.

The author is right, the only vitamin that is necessary in a whole foods plant based diet is b12 but as a meat eater like yourself you should probably be getting that supplement as well since it’s not found in flesh or dairy.