From pure statistical reasoning, or even taking into account basic physics (e.g. speed < c) and biology (e.g. speed > 0, almost certainly speed << c), you can't conclude anything about the average speed of an alien species by finding out that one individual can run as fast as Usain Bolt.
Maybe not much more. But definitely more. And not with 100% confidence, we can't conclude anything. But there is information there, and we would be daft to ignore it completely because it isn't conclusive. We should adjust our predictions.
> "you can't conclude anything about the average speed of an alien species by finding out that one individual can run as fast as Usain Bolt."
If you know that a sloth takes 6min40s to cover 100 meters, a giant ant takes 1min40s to do it, and you run it in 30 seconds and a cheetah can do it in 5.1seconds. I say "I'm thinking of a creature, what is it?" your answer has to be "I don't know". If I say "an example of the creatures I'm thinking of takes 9.58 seconds" you ought to be thinking "slow cheetah or fast human" not "could be a sloth because ackchyewally the distribution of sloth speeds could be very wide so we don't know".
You could assume the individual was the fastest of their species, but why would they be? You could assume the individual was noteably slow, a famous creature to be laughed at. With no way to know which is the case, you may as well assume the creature is a typical example - not because you know they are, but because if they aren't you have no way to know which way they aren't.
Before we knew nothing, now we have more information than nothing. We ought to update our predictions based on this information, even if it's not much information and we can't know for sure. We ought to think the alien is less likely to be an immobile plant or silicon intelligence, less likely to typically move at the speed of a sloth. Not impossible, but this isn't meant to be a trick question where we get a deliberately wildly misleading time. 9.58 seconds is more like (cheetah, human, giant ant, jellyfish) than it is like (panda, mushroom, saltwater snail, sentient light beams). And yes, there might be nothing like those creatures at all, but "we could be wrong" is no reason not to adjust our best available guess.
[1] https://www.newscientist.com/article/2220211-desert-ant-runs...
From pure statistical inference, you know precisely 1 more thing than nothing: an individual of the species can run 100m in 9.58s.
Now, adding other kinds of information and reasonable assumption from physics and biology, we can conclude more than that 1 thing, as you say. It's unclear exactly how much those would apply to alien biology, but they might.
And if I then told you one example alien covered 100m in 9.58 seconds would you not change your estimate at all from learning that information? You wouldn’t assign less probability to nuclear powered teleporting aliens or crawling vine plant aliens or insect sized slug aliens because “you can’t say anything without knowing the distribution”?
No that would be silly; you would put a lot more weight on times around 9.58 seconds, because that tells you something.
Saying “it doesn’t tell you much” is right but it’s told you something, there is non-zero amounts of information there.