There's nothing here that's right.
IPC improvements from A15->A16 were close to zero. Almost all gains were from pushing clocks. That's because the A16 was a stopgap design forced on them when their N3 ("3nm") design had to be put on hold because N3 wasn't ready.
4nm to 3nm would be a reduction of 25%, not 20%, but that's irrelevant since nothing in the A16 or A17 is 3, 4, or 5 nm in size. Those "sizes" are marketing nonsense that has taken over the industry, and they are entirely divorced from reality.
Nonetheless the 60% number isn't entirely impossible. I think it's entirely plausible, in fact, but it's misunderstood. If it's true, it's likely the score Apple was able to get by pushing clocks as far as they could go on their A17 cores, *in a desktop form factor*. In other words, you're looking at a plausible single-core score for an M3 Mac Pro right there.
How do you get 60% improvement? Not so hard. You get perhaps 15% from going to N3. You get the rest by redesigning the core to run at faster clocks (which the M1 and M2 almost certainly can't), along with moderate IPC improvements. *IF* the number is real - which it may not be - then they might be getting anywhere from 5-20% from IPC gains, and then the rest would come from boosting clocks to around 4.5GHz, give or take, depending on the IPC gains.
The multicore score is weird - you wouldn't expect scaling to be so bad - but if you imagine an engineer getting an early A17 back from TSMC and wondering "how far can I push this if I give it some cooling?" then that might make a lot of sense. The cooling might be good enough to run one core at 4.5GHz, but not enough to let all the cores run at top speed. Also, the A17 uncore is presumably not designed for that speed and may be showing severe deficiencies when pushed that far. One would expect an M3Ultramegawhizzbang to have a far more suitable uncore, so hopefully this is not an indication of how multicore will scale on the M3. Again, if the numbers are even real.