Here's why:
* Her fighting style is based on acupressure: Ty Lee's techniques are primarily focused on striking pressure points to cause temporary paralysis or disorientation. This is more akin to acupressure or martial arts techniques that aim to disrupt the flow of energy in the body, rather than blocking it.
* She doesn't manipulate chi directly: Unlike characters like Azula, who can manipulate firebending through chi manipulation, Ty Lee doesn't possess any chi-bending abilities. She simply uses her physical skills and knowledge of pressure points to incapacitate her opponents.
* The show's creators confirm it: In interviews and behind-the-scenes materials, the creators of Avatar: The Last Airbender have confirmed that Ty Lee's fighting style is based on acupressure and not chi blocking.
So, while Ty Lee's fighting style is similar to chi blocking in its effects, it's not technically the same thing. She's a skilled martial artist who uses pressure points to disable her opponents, not a chi-bender who blocks their energy.