I think the OP's interpretation of this is wrong. Just because someone was found to have an equivalent of ingesting so and so much, after UV radiation, doesn't automatically imply that it a good idea to ingest any amount of vitamin D. Ingestion is different from exposing skin to UV/sun. The paper probably doesn't state, that ingesting that much will make a person absorb that much from that ingestion, nor does it state, that ingesting some equivalent amount will be safe and without side-effects.

So the paper may be well researched or whatever, but the interpretation of it is questionable.

What you have given is rather a comparison, that doesn't stand up even the slightest scrutiny, and an improper citation. I am not gonna read a whole paper on a whim. Cite properly, with proper hyperlink, and at least a page number, and I will consider looking at it.