Eh, that's part of it, but a lot of it has to do with the M1 having very very high IPC (much higher than comparable x86-64 parts), meaning they could run the chip at a much lower max clock speed (3.2 GHz versus boosting to 5 GHz for most competitive x86-64 CPUs) for similar overall performance.
This makes a huge difference because power consumption increases exponentially with clock speed.
edit: thinking about how it relates to Intel's process–architecture–optimization, it feels a bit tricky to compare. Apple's process seems to be something like: architecture(A-series chip for iPhones)-optimize-with-new-die-reusing-basic-cores-in-diff-arrangement-targetting-perf-in-small-thermal-envelope(M1 for iPad Pro and small Macbooks)-optimize-again-with-another-new-die-reusing-basic-cores-but-in-yet-another-arrangement-targetting-perf-in-a-wider-thermal-envelope(M1 Pro/Max/Ultra), and that all happens before you get to the next M-series increment, which begins with an A-series increment.
So the M2 is less the optimization of the M1 than it is the re-use of the cores in the new A-series chip preceding it, which was an architectural change, plus optimizations and other SoC differences.