So they resurrected old code from the Newton?
My guess is they resurrected and probably improved the Ink framework which used to be on Macs back when Macs were still 32-bit - they never upgraded it to 64-bit, and it doesn't look like it's in macOS 14 either (no prefPane, no Framework, private or otherwise). That in turn was based on the old mothballed Rosetta code in the Newton 2.0 that they probably should have stated with in the original Newton, though it might not have been in working form at the time. (The original was in 1994. N2000 was in 1997.)
<newton rant - how Apple could have maybe trounced Palm Pilot and well.. everyone>
As well putting a better (read reasonable) processor in the first generation. The StrongARM (162 Mhz, 185 MIPS) in the Newton 2x00 wasn't released until 3 years after the first Newton, but there were other ARM chips/speeds. The original H1000 used to lowest speed ARM 610 at 20 Mhz (17 MIPS), but the highest speed was 33 Mhz (27 MIPS).
The N2x00 StrongArm (162 Mhz, 185 MIPS) can be overclocked to 220 Mhz (~253 MIPS). The specified top speed of the StrongARM is only 200 Mhz (230 MIPS), but you can apparently overclock to 220 [1]. Who knows, you might be able to go even higher than that, though possibly with a custom designed case with heat fins and a small fan, and not-so-occasional random shutdowns.
[1]
http://web.archive.org/web/20101212092417/newton.tek-ed.com/newtspeed/
More memory/maybe faster memory bus (not sure whether they could have gone higher) wouldn't have hurt either. The original had a pitiful 640KB RAM while the 2100 had 8 MB. The Newton ran programs execute-in-place on the flash card, so RAM burden was reduced, and data storage was largely if not entirely virtual-memory flash based. A better display than the original might have helped - certainly a bigger one the size of the 2x00 (though small screens have their charms - as some iPhone users can attest). Two PCMCIA slots in the first machine would also have been a plus - one for communications, one for storage or other (but probably impossible given the form factor.)