If they observe a day or do not, do it for the Lord and give Him thanks, then it’s good in the eyes of the Lord. Same with food. Condemnation of fellow Christians for those same things? Not so good. Putting a stumblingblock before their brother, is how I believe it’s described.
Observing feast days and dietary laws can lead to greater understanding of certain Biblical matters, the prophetic in particular though, imho. There is good in it. I won’t criticize someone who feels so led, personally.
The point of the article is a "church" that teaches it is absolutely required - not someone who "feels so led" - and that Christians not teaching this are Counterfeit Christians.