Nothing wrong with that article. It is your conclusion that is incorrect.Did you not read this and the associated article by Dr. Sakas? Dr. Sakas was an important and very well thought of veterinarian, before he died from Covid last year.
" Vitamin D3 is required for the absorption of calcium into the bloodstream from the intestinal tract." So that intimates that D2 does not (there are only two types of D of any consequence - D2 and D3.)
What you posted actually that does NOT “intimate” that d2 doesnt do anything. That is not how the relationship of d2 and d3 works. Also that does NOT answer whether d2 is bioavailable or not.
To continue this conversation, I really need that info confirmed. Otherwise I am going to assume this is another piece for forum logic that should be disregarded. And ask that you stop sharing incorrect info.
So a good source for the bioavailability of d2 for avians, please.