I would not put too much stock into James Hoffman's confident assertions. He claims to be able to taste difference between different coffee grinders - but doesn't do it in a blind test.
YMMV of course!
One thing to add: If you want to think even less in the morning. Just weigh the beans and water with a kitchen scale. 18 gr of beans, 160gr of (boiling) water (basically a 1:9 ratio regarding on the size of your basket).
Maybe that's exactly what you noticed. I cannot think how starting from already hot water vs. letting the water warm up and boil from the stove, could make any noticeable difference.
The idea is just that the beans don't get cooked as much by the heat ahead of the brew phase. For me it's made a big difference.
High-end (specialty coffee standard) commercial grinders produce a tighter variance amongst the ground coffee particles which leads to a way more even extraction, i.e. a more pleasant and balanced taste in the cup. Perhaps the most common model is the Mahlkonig EK43S, which is a ~$3,000 grinder.
Home grinders are far cheaper, in the range of ~$75–300 or so for popular ones, and tend to produce a broader variance of particle sizes which leads to big particles ("boulders") getting overextracted, thus imparting bitter flavors; and small particles ("fines") getting underextracted, thus imparting sour flavors. The higher quality and lighter roast your coffee is, the more noticeable the impact of the grinder is.
You don't have to take James Hoffmann's word for it at all, this is standard issue coffee grinder theory 101, which any specialty coffee professional would agree with. It's also easily testable at home, even if you haven't experiencend it in an experiment context. I took a short class on the theory of coffee once and the major experiments were comparing the same beans ground across different grinders (and then with or without use of a coffee sieve for further refinement) and the same beans across different brewing methods and techniques. The particle size distribution from the grinder is one of the most important variables in the whole process.
Yes, as an example his lack of reviews on eureka grinders is very noticeable in comparison videos.