Pythagoras is best known for the Pythagorean Theory, which has to do with triangles, and so, mathematics and geometry. Rhinos know nothing about all that.
What We do know is that nobody knows when Pythagoras’ was born. We chose today, though there is every chance We are mistaken. Even so, We can wish him well, if not Happy Birthday.
Your Inner Rhino looks on the bright side whenever possible.