It was only the first reasonably portable computer that did not have an astronomical price, so it was accessible for many people.
The first reasonably portable computer was the GRiD Compass "briefcase computer" (i.e. that could be carried inside a briefcase; the word laptop was coined later), which was introduced in April 1982.
GRiD Compass was the first portable computer made in the clamshell format now used by any laptop and the first portable computer with a flat display instead of a CRT (it had an electroluminescent display).
GRiD Compass looked like a modern laptop (unlike all the previous portable computers, which were large boxes with handles, usually compared with portable sewing machines), but it did not have an internal battery, it had to be used with an external power inverter where mains power was not available.
It used an Intel 8086 CPU, but it was not compatible with the IBM PC, as it had different peripherals.
Because it was extremely expensive, it was typically used by customers with deep pockets, e.g. the NASA Space Shuttle and special missions of the US military or CIA.
We're running into terminology territory which is rarely productive, but let's go with it. There are multiple reasonable takes on this so I'm not looking for a fight, but for me I'd classify the Model 100 as a mobile devices. It's a bit on the large side for that classification, but no more so than a modern tablet except for the thickness, and you could conceivably us it standing up.
For me a portable computer is one that needs a table or lap to use (can't reasonably be used standing up) and replicates the capabilities of a desktop computer in a more compact form. The T1100 is beaten out on that definition by the Osbourne, though arguably that's in it's own 'luggable' category. I think the T1100 is almost certainly the first computer we could call a laptop though.
I got my "portable" computing start by travelling around South Asia with a Sharp PC-5000 (1983; https://en.wikipedia.org/wiki/Sharp_PC-5000) in a briefcase. Those were the days...!
[edit: And what did we do with such a machine? Created text-editing/printing software for scripts like Devanagari, Urdu, and more.]
Oh wow. I a Sharp PC-5000 to write software (that would be sold with a PC-5000 as part of the package) that interpreted data from primitive vascular ultrasound and angiodynography machines. It had a built in printer that wasn't the fastest, used a bizarre "bake on" thermal ribbon, but was higher quality and larger than the built in printers in the lab equipment. Was completely obsolete one year later.
That's also very cool, despite being superseded. Amazing the things a primitive machine could do.
Yeah - the Sharp's (optional) built-in thermal printer was much higher resolution (with a 24-dot print head, resulting in around 200dpi IIRC) than most dot-matrix impact printers of that era (8- or 9-pin print heads, 70dpi or so), but the thermal ribbons it used to print on plain paper were hard to come by. You could also use it with thermal paper, but the resulting printouts tended to fade quite quickly (somewhat depending on the environment).
We were thrilled when we managed to get hold of 24-pin impact printers that produced more permanent output, and where we could re-ink the ribbons. Produced camera-ready copy to publish books with those for several years, designing "oversized" fonts that were printed using multiple passes, and then photo-reducing the printed output to boost the effective resolution.
I always wondered what I should call the TRS 100/Kyocera type non-foldable portable computers (and now the arm powered DevTerm) and I kinda settled on "A4 computers" since they're apparently about that size.