1% seems to be a small number in your mind, I guess. Take one million people and if the chance to hit the jackpot is 0.1% you still get around one thousand people, who are lucky enough.
Maybe everthing changed, but in the early days of online poker, 6 or 7 years ago, we said that you need around 600k hands to have some(!) trust in your win rates (your Big Blinds per hundred hands, to be precise).
100,000 hands is nothing. Ask any long time pro who understands the game. I've personally known several who play a very consistent, disciplined style against a consistent level of opponents whose results would vary greatly across 100k hand sets, from being a huge winner to barely breaking even to losing even though they all were at least steady winners overall.
When you get in the 500k+ realm, it starts to get more reliable, but even streaks of this size are possible at the statistical fringes.
Let's say you came out even after 100,000 hands. If I randomly divided those hands into two sets of 50,000 each, would you expect one of those sets to be up by 10% and one of those sets to be down by 10%?
Not sure I understand your other question. There are no percentages in particular that I would 'expect', but if you ran the sim enough times then yes they'd revert to some mean. I've never done such analysis so I don't know what the results would look like.
Luck on these bigger pots has a huge impact on overall win rate, but in a set of 100,000 hands, you may only be involved in 2-3000 of them, and you may only expect to win something like 400 or 500 (very rough estimates). Maybe that helps explain why there's more variance than you might expect in a seemingly large sample.
This cannot possibly, possibly be true. The expected deviation goes as the square root of the sample size, which means that the percentage deviation goes as the inverse square root of the sample size, which means that if you play thousands of hands a day for a year, your deviation ought to be less than 1%.
Anything that persists over 100,000 samples is not luck.