It says he drowned... assumed because of the reason OP gave. Besides, moot point giving you're referencing Wikipedia to begin with.

> Hippasus is sometimes credited with the discovery of the existence of irrational numbers, following which he was drowned at sea. Pythagoreans preached that all numbers could be expressed as the ratio of integers, and the discovery of irrational numbers is said to have shocked them. However, the evidence linking the discovery to Hippasus is unclear.

> Pappus merely says that the knowledge of irrational numbers originated in the Pythagorean school, and that the member who first divulged the secret perished by drowning.

It also says “one writer even has Pythagoras himself "to his eternal shame" sentencing Hippasus to death by drowning, for showing "that 2√2 is an irrational number”.”

was drowned was the version I heard in school.