"Source from animal" is not equal to non-vegetarian.
源於動物 can also be vegetarian, e.g. milk.
however, not all plants are vegetarian, e.g. 五葷
For buddhist texts,
we also need to see if the statement represents Buddha's opinion or the monks' opinion, or the translator's opinion. Besides, English translation is far better than Old Chinese traslation.
In history, there is mentioning of Buddha drank milk too.