The article appears to be basically accurate, although I found its organization and presentation a bit unhelpful. The author says he's going to compare 2017 Opening Day payrolls to 2017 Opening Day payrolls. OK; but then he veers into discussions of individual teams, groups of teams, etc. He's completely buried the lede, if the headline indicates what he's trying to communicate. It isn't until you get to nearly the end of the piece that the author mentions the overall change in payrolls, and then it's in one sentence, almost a throw-away. And based on the numbers in his team-by-team tables, his overall numbers are slightly off.
The real, overall story: Overall Opening Day Payroll dropped from $4.1 billion in 2017 to $4.05 billion in 2018, a decline of $55.4 million, or 1.35%. The author assumes that overall MLB revenue is increasing by about 5% (a reasonable assumption, but of course we don't know), and concludes that player compensation as a % of revenue is declining (which it probably is).
I found all the stuff in the first 3/4 of the article to be...well frankly, just noise. The only important information here is the overall change, which the author barely addressed. Team-by-team payrolls should be expected to fluctuate up and down, as teams go through development/competitiveness cycles; overall payroll, relative to overall revenue, is the only thing that's relevant to management-labor issues (which is the subject that drives this article).
Moreover - and the author doesn't address this at all in the article - the longer-term issue is whether the 1.35% decline in overall 2018 payroll represents the beginning of a trend, or whether it reflects some kind of one-time correction. One might argue that what we saw in the 2018 free agent market was - finally! - a recognition that overpaying players in their 30s for performance in their 20s that they have little hope of repeating in the future is foolish. If that is the case, one would perhaps expect to see a bit more correction in the next couple of years, as players in their mid-30s come to understand that they've reached retirement age, followed by a resumption of salaries tracking revenues, albeit with an overall younger player base.