That certainly is not true. Arab historians in their chronicles have made a distinction between bilad (countries) of Sindh and Hind, refering to Indus basin and Ganga-desh respectively
Let's see it in a way people would understand Babylonian World Map ca. 600 BCE: (No Mention of Indus or hte big continents only focussing on the Fertile Crescent) Map of Anaximander ca. 550 BC: (Shows Asia but not much else for our relevance) Map of Hecataeus of Miletus ca. 500 BCE...
Anyways so you do agree Hind refers to modern day India...and Sindh to Pakistan?