No, no it's not. It's not hard to understand why the emperor minting a 40% gold aureus isn't going to reduce the value of my hoard of 80% gold aurei.

On the other hand, a fiat currency issuer doubling the money supply can (not necessarily will![1]) indeed reduce the value of any fiat I hold.

And incidentally coin debasement in the late Empire was largely due to the empire's economy and thus need for currency growing and exceeding the available supply of precious metals. If only they'd had double-entry bookkeeping...

[1] This is because money can't cause inflation, ie drive up prices, unless it's actually used to bid them up.