I have a few thoughts of my own on the subject, based on my own work situation, and they don't quite line up with theirs.
First off, yes... I would say that at least for our workplace, stress levels in I.T. have generally increased over the last few years. (I work as part of a 4 person I.T. team for a marketing firm that has several locations strategically placed around the country, close to the majority of clients they have or want.)
Marketing is definitely a business where lots of millennials are hired. Our I.T. group and upper management are really the only people in the company of an older generation than that, other than a few random exceptions.
But to claim the I.T. stress levels are correlated with the millennial generation's lack of in-person communication skills? No... at least for our industry, that's not the case at all. You can't be successful working in marketing for us if you're not an exceptionally good in-person communicator. I know I'm far less comfortable chatting up random people in social situations than any of the millennials we've got working as creative directors, producers, designers, etc. Maybe we're constantly hiring the exceptions to the rule because of the nature of the business ... but regardless, that's the situation for the people our I.T. group supports.
Where I see stress levels climbing has more to do with people expecting more and more from the computerized tools they're given. For example, when I started working for these guys, several of our offices literally spent 90% of their day buried in Outlook. Everything revolved around email correspondence and scheduling meetings or appointments. Sure, they had the occasional need for the rest of the Office suite (especially PowerPoint or Keynote for our Mac users, if they were preparing a presentation for a client), but the vast majority of support calls or issues were "Why did my email bounce?", "It says my mailbox is full!", "I can't find this message I know I saved someplace in here earlier today.", or "So and so received my calendar invite 3 times in a row for some reason." Stuff like that, along with trouble opening various email attachments they received.....
Looking at how things have evolved now? We ran into issues where some of the huge Word templates they use regularly to produce client proposals got too big to keep editing reliably inside Word. (Lots of copy/pasted graphics in them and all that.) So we now paid for a cloud based service designed just for such proposals. Instead of constantly filling mailboxes with email attachments getting shared around, we set up DropBox for Teams so I.T. creates any of the "top level" folders anyone requests and makes sure the proper folks are given read or read/write access to those shared resources. As we've grown, the Finance department required better automation so they could process all the invoices in a timely manner as offices generate them. So they put in dedicated scanning stations at each office with document capture software that goes to "watched folders", with special software that can toss them into their accounting system as it sees new ones appear. The original few, designated office people with copies of Adobe Acrobat (full version, not reader) kept growing as more users saw the benefits of being able to actually edit a PDF document on their Windows PC (or saw Mac users doing it natively with Preview and asked why they can't have the same capabilities). So that led to buying Creative Cloud with user accounts I.T. again has to manage.
On top of that, one of the offices is trying to get more serious about offering in-house video rendering capabilities instead of outsourcing it all the time, so now we're starting to build and support a rendering farm and high end video packages on the clients.
What we haven't done is hire a single new I.T. staffer to help with any of this.... We push for it all the time (especially when one of us is out sick or on vacation and the pressure is really on). But at the end of the day, management feels like it's not cost justified. People are still generally happy with our level of support and when they complain that tickets aren't resolved in a timely enough manner, management tells them they need to just be more patient with us because it's too costly to hire enough staff to shorten those delay times.