Religion wise though article claims an Egyptian link which is new to me, it has some clear Hindu associations like the Pasupathinath seal
https://en.wikipedia.org/wiki/Pashupati_seal
Script wise the contention and claim also comes from Tamil and Sanskrit. TED talk on this below
You could call Rudra/Shiva as modern versions of that motif. But calling the figure in Pashupati seal as depecting a Hindu deity is probably not correct. IVC was pre-vedic after all. No doubt later cultures adopted IVC deities into their own pantheon. But IVC religion was likely very far from what we recognize as Hinduism. And probably closer to religions in Mesopotamia at the time. Egypt does seem further culturally than Mesopotamia to me though. So I find the Egyptian connection a bit tenuous as well.
There has been historic and ongoing synthesis which very often follows embrace, extend, extinguish pattern, so the GPs characterization is misleading.
These ideas probably gain traction from the Sramana traditions which also gave rise to Buddhism and Jainism.
It is hard to tease apart the influences exactly, esp in the case of IVC where very little is known about the culture. But some iconography bears a striking resemblence iconography found in indian religions at a later date.