The fact that a lot of Chromebooks are being sold is fairly solid; I would reckon that the questionable claim is that Chromebooks have strong sales traction with retail consumers. I bought myself a Lenovo Duet tablet last fall because I wanted a device that could last multiple days with intermittent streaming use and I missed the feeling of a cramped 10" netbook. I got it on sale for $200 USD and was floored by how nice the experience was on a PC that cheap. But friends and family who saw me with the tablet were shocked that I, an adult who likes computers, owned a Chromebook. I only know one other person IRL with a personal chromebook, and they bought it after being given a school-deployed one in college.
I use one and have had a couple over the years. Decently cheap and I functionally just want a laptop form factor and UX for a tablet use case: web browsing, some light app usage (often for casting / streaming), and also being able to type as needed, all from an actual couch / on the lap / wherever. Used to be no Android App support so that part was a no go and now you have the linux containers to fall back on if you need to run something else or want a proper terminal.
I have a bulky work laptop and a big desktop PC. The niche left over maps to a nice slim, fanless device for casual usage very well in the Chromebook space. Maybe preaching to the choir here, but my keyboard will need to be pried from my cold, dead hands and the tablet + detachable options all seemed way too delicate.
My anecdote: A lot of people seem to be using Chromebooks to replace tablets (because good, non-Amazon tablets that aren't expensive are rare these days). You can pick up a $250 touchscreen Chromebook that works as a vastly superior web-browsing and video-watching device than a $250 Samsung tablet.
Keep in mind that the majority of all fed gov visits are USPS tracking pages and the like. Chromebooks are majority used by students so I would expect this.