It is a known and proven fact that the ocean absorbs CO2, which is removing a greenhouse gas and thus has retarded the warming that would have otherwise taken place. However, it is not necessarily for the hiatus and the article doesn't state that it is. It's been going on in the background all along. In other words, this isn't a new development, it is just part of what the ocean does.
We know about past acidity from air bubbles trapped in ice due to atmospheric CO2 levels being some equivalent amount of oceanic carbonic acid levels (there is an exchange back and forth between the two, see that carbon cycle illustration I linked), as well as coral and other organic proxies that are sensitive to the pH of the water and leave behind evidence.
On your second point: the article actually doesn't claim the new technique is showing more acidification. Previous techniques, which involved monitoring buoys, readings from ships, moorings, ports, etc. have shown decreasing pH (increasing acidity) over the last 2 or 3 decades. This new technique is able to use existing satellites to monitor pH from space globally, rather than using point data from instruments scattered about the Earth. This will allow more robust monitoring of ocean pH. Also, the satellite data confirms the surface point data. The article never states, so far as I can see, that the new technique alone is showing more acidification, but rather is improving the way we can monitor the already observed increasing acidification. The new data is more robust and accessible, but the trend and phenomenon was already known.
Here's a redundant article, that is perhaps more clear:
Satellite images reveal ocean acidification from space | EurekAlert! Science News
To your other criticism, I agree to an extent. Just keep in mind the ability of sea water to absorb and dissolve CO2 is largely a function of temperature. Warming oceans and temperatures actually means LESS absorbing of CO2 in the future, meaning more remains in the atmosphere. Now, the oceans will be acidic enough at that point to be a major problem ecologically and economically (fisheries), and on top of that the rate of carbon dioxide accumulating in the atmosphere would be increasing even if the amount being released was steady. So yes, I agree that the author conflated the two when she called it an ongoing danger of climate change. But as you can see there is a relationship between these two things, even if it is actually environmental change (which is a broader category that climate change fits into).
This really comes down to a poorly worded sentence or two, which is understandable that this author has a background in psychology, not any sort of physical science. I have been thinking that I should try my hand at science writing for awhile now.