Overall, this article is quite reliable.
Firstly, it is reliable in being peer-reviewed by a medical expert. This article mainly explains the way that caffeine may help to reduce headaches caused by run-of-the-mill tension, migraine, hypnic, and caffeine withdrawal while causing headaches because of too much caffeine, caffeine sensitivity, medication overuse, and dehydration. Since the topic is largely about the medical aspect, the peer review of an expert who studied medicine increases the reliability of the article.
Secondly, the article is quite balanced, mentioning opportunities for both sides. While explaining the logic behind caffeine can help to reduce headaches, the author also admits and spends nearly half of the length talking about the possibilities of caffeine-causing headaches. Having presented explanations and arguments from both sides, the author seems balanced and impartial, which increases the reliability.
Lastly, public consensus helps to further increase reliability. UCLA Health had a post that basically says the same thing as this article. Again, an essay from Zdunska published by the National Institutes of Health also agrees on the point that caffeine can both relieve and trigger headaches.
Yet, there are some flaws in this article. For instance, the article doesn’t offer any references or citations where the author gets the data from. This might decrease the credit of the author.
https://www.uclahealth.org/news/article/caffeine-connection-between-coffee-and-headaches
https://pmc.ncbi.nlm.nih.gov/articles/PMC10385675/