No — Babylonian scribes were using it at least 1,000 years before he was born.
A clay tablet known as Plimpton 322, dated to around 1800 BC, lists sets of numbers that fit a² + b² = c². Mathematicians in India and China knew the rule independently too. Pythagoras (or his followers) may have been among the first to prove it in general, but the relationship itself was already ancient.
