|Drosophila melanogaster. Source: Wikimedia Commons.|
Now the ability to react differently to stimuli, does not mean that organisms with less brain power than humans are sentient. Sentience is the ability to be self aware, and to understand and think critically about yourself and what goes on around you. Whether or not organisms are sentient - and to what extent they may be so, remains a controversial topic.
Flying left instead of right when poked isn't the same thing -- at all. But it does suggest that we still have a lot to learn about the brain, even in teeny tiny organisms, because researchers have only scratched the surface of understanding the ability to make choices, and what it means about the capabilities of the brain.