It is both skill and luck,
luck: the timing window to get a +100 is 0.2 pixels in each direction, meaning 0.4 total, notes move at 200 pixels a second. At the game’s fps limit that’s 200/144 ≈ 1.4 pixels per frame
0.4 / 1.4 = 0.288 = 28.8% chance a +100 CAN be hit
9 in a row: 0.288^9 = 1 in 73000
the second part of my comment was about skill, at 8 ms of standard deviation (which is pretty much the human limit, his is probably much higher) the chance of hitting a perfect note is 2 * Φ(1/8) - 1 ≈ 2 * 0.5497 - 1 = 0.0994 = 9.94% (https://www.calculator.net/z-score-calculator.html?c2z=0.125&c2p=&c2pg=&c2p0=&c2pin=&c2pout=&calctype=converter&x=Calculate#converter)
So hitting 9 in a row would be 0.0994^9 = 1 in 1.055 billion (yes, I got this slightly wrong from rounding errors)
To get 9 100’s in a row, you would need to get 9 perfectly positioned notes (1 in 73000), and then hit those 9 perfectly positioned notes at the perfect time (1 in a billion at the human limit), combining to around 1 in 73 trillion.
If you were to hit 1000 notes a second for 24 hours a day with the human limit of precision, it would take you 2300 years to get 9 100’s in a row
FAQ:
Yes, this is just an explanation of my previous comment.
Yes, I decompiled the game to get the scoring logic
Yes, I saw the message in the code
Yes, I am writing all this because I’m bored
Yes, I am also writing all this because I don’t believe opgrhythm
tl;dr: at the human limit, you would need to hit a 1 in 73 trillion chance to get 9 perfect notes in a row. Also input delay n hardware stuff that make that chance even lower.