First, I'm not complaining about anything. I do not give a fuck about whether India manufactures stuff or not. But there was a question about a number, I provided an answer for how it could be derived. You're welcome!
I disagree with your objection. Actual current output is a great proxy for actual current manufacturing capability, assuming even a tiny bit of rationality. If the two are not linked like you imply - and in fact India already has as much capacity as China - then somebody built 10x more factories than they needed, and lost unimaginable amounts of money doing so. Is that what you're suggesting happened?
Now, the claim is not that the factories, supply chains, trained workforce, etc could not eventually scale to the same size in India as in China. But somebody actually needs to do that work. Until it is done, the capability possibly does not in exist.