I assume a lot of that information comes from the Machine Identification Code [0], the "yellow dots" emitted by almost all printers.
There's a number of encoding schemes [1], though most of those only identify the printer - they don't go far enough to identify the graphics card or OS where it originated. That's a new capability - if it's being accurately relayed here.
Indeed if they had the identification code they would have been able to pinpoint the model and serial number of the printer, but they haven't released that information -- only that it is a HP printer with HP 302 or 304 model ink cartridges, which I assume is based on analysis of the chemical composition of the ink.
To my knowledge only laser printers participate in the MIC scheme. While the boundaries of the program are somewhat unknown, just from a technical perspective inkjets generally struggle to produce low enough coverage for the marks to not be pretty visible to the eye (bleed of inkjet inks prevents high-pitch halftoning performed by laser printers to produce very low coverage).
Identifying the graphics card/OS doesn't sound impossible.
They figured out it was Wordpad (presumably based on line breaking or similar) which narrows it down to Windows, and the graphics drivers probably subtly affect the font rendering in the same way that can be used for canvas fingerprinting.
That said, Windows 8 or 10 using Wordpad and Intel integrated graphics doesn't exactly narrow it down.
The printer, which was likely bought with a credit card and whose serial number was documented when purchased or when installing drivers that phone home with IP address, location, etc.
There's a number of encoding schemes [1], though most of those only identify the printer - they don't go far enough to identify the graphics card or OS where it originated. That's a new capability - if it's being accurately relayed here.
[0] https://en.m.wikipedia.org/wiki/Machine_Identification_Code
[1] https://dl.acm.org/doi/10.1145/3206004.3206019