From a Jain perspective, no — Jainism and Hinduism were not truly indistinguishable.

There may have been times in ancient India when:

• people lived in the same cultural environment,
• some customs looked similar,
• gods, rituals, and social practices overlapped,
• and many later communities used shared language and symbols.

But Jain Dharma has always had its own distinct identity based on:

• Ahimsa in its highest form,
• Karma and liberation through self-discipline,
• the teachings of the Tirthankars,
• non-acceptance of a creator God as the cause of the universe,
• and a unique path of ratnatraya: right faith, right knowledge, right conduct.

So, while there may have been cultural blending at different times, Jainism was never the same as Hinduism in its core philosophy and spiritual goal.

In short: Shared environment, yes. Indistinguishable, no.