I disagree. If all of the manufacturers mentioned in that article can manage just over a million a year together, that's a declining market.
There is a bit of hyperbole that the core of the workstation market was actually made up of many millions before. Not really. There are oscillations when the world economy goes up/down. There has been some periods where the workstation has been more stagnant than declining. The overall workstation market is not a significant growth zone overall though. Largely a zero sum game of treading water with limited set of clients.
I remember when big commercial/financial printers would have several hundred PowerMacs in use at a time.
200 at 400 printers is only 80,000. That is two orders of magnitude off of millions. Throw on top they were not buying 200/yr. Most likely they accumulated a limited fraction of those every year and this is looking at the end result of a multiple year build up. Then to make things worse in annual count these tended not to get retired. Probably a few of those shops where can see the same PowerMac still be used alongside the same printers they were attached to. If replacement cycle is 8 years than that 80,000 looks alot more like 10,000 which isn't much. I think there was a vendor putting mac minis in to vending machines in that range. [ nevermind that for what computing those dated printers need can probably be done by a modern mini. ]
Sampling this small niche doesn't really shed tons of light about what the whole market is doing.