I have added negative delta by shorting stock, buying other puts, selling calls, buying put back spreads, buying put spreads and in some cases...
So a 10 B imbalance is not a big deal to you. Wow !
I doubt that 99% of orders are generated electronically, filled maybe but not generated. Besides very large options transactions are done OTC.
A seller came in at the market. You got lucky.
In my opinion paper trading is deceptive so in testing a new trade I reduce position size and see how it works for real.
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