That is ill-informed nonsense. Of course it’s a noun. Point the tweeter in the direction of Alexander Pope’s couplet, both for the usage and the sentiment:
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring.
It is not entirely clear whether the tweeter had the plural form particularly in mind, but, if so, its use is not unprecedented. In Cymbeline, I. i. 43 the First Gentleman says:
The king . . . Puts to him all the Learnings that his time Could make
him the receiuer of.
Francis Bacon uses it at least twice:
Particular and positive learnings of lawes doe easily decline from a
good temper of iustice.
He did send his diuine truth into the world, wayted on with other