The full answer
No.
Grass-fed describes the animal's diet.
It does not tell you who slaughtered the animal, whether Bismillah was pronounced or whether the Zabiha requirements were fulfilled.
Grass-fed and Halal are two completely different questions.
Answers in the Halal Knowledge Center reflect the standards followed by Halal Monitoring Services (HMS), which operates as part of the Shariah Board of America. HMS certifies only what it checks.