Some would argue they are the same thing...but the differences between the two are subtle and vary by degree.
For instance a texlax is a relaxer that is left on for a shorter period of time than your traditional relaxer. Your purpose is not to get the hair bone straight, but to straighten it out just a little. With a texlax, you can wear your hair straight or wear a wash n go.
Texturizer, again is a relaxer that is left on for a shorter period of time than even the texlax. The texturizer loosens the curl pattern up; just a bit. Some women with texturizers still have the look of natural hair as a lot of the texture is still left.
Again, they are all relaxers...just a matter of degress separate them:
Relaxer (Straight)
Textlax (Semi-Straight)
Texturizer (wavy/curly)
HTH