That little article is far from thorough. I don't know the law in all the states and territories and you don't either.
The point you just pass right over is that no primaries have been held yet. And people who cover politics for a living are constantly asking Trump if he would drop out and run third party. So, that possibility is there.
I'm sure Trump has several months to decide whether to stay in the Republican race or drop out and start qualifying for the state ballots as an independent.
You're just muddling this discussion and have no specific facts.
He could drop out of running this year, and run as an independent, yes.
But most are asking if he loses the primary, or insinuating that question.
If he runs in the primary as GOP, he cannot get enough electoral votes to win the general as an independent.