Speedrunners are very well aware of all the probability based events of the games they play, as well as the odds of those events and any circumstances that can change them [0]. It's called 'luck manipulation'. Usually that's only really useful to tool assisted runs, but on occasion luck manip can be performed by human players.
Regardless, while those in-the-know can recognize that a good run would have been a record if not for an unlucky event, at the end of the day all that matters is your time (or score). Accounting for the randomness is part of the strategy aspect of the sport.
[0] People who speedrun a particular game will also know of any differences in those probabilities across all known versions of the game. These people have studied these games so deeply they usually know more about how they work than the people who made them.
Regardless, while those in-the-know can recognize that a good run would have been a record if not for an unlucky event, at the end of the day all that matters is your time (or score). Accounting for the randomness is part of the strategy aspect of the sport.
[0] People who speedrun a particular game will also know of any differences in those probabilities across all known versions of the game. These people have studied these games so deeply they usually know more about how they work than the people who made them.