This is not so. There is no magical property of currencies that automagically change the value of other currencies. If I started printing bills of a new "robm dollar" currency right now I would not affect any other currency in the world, no matter how many or how few I printed.

If I could convince some people to accept robems for a good, a service or another currency I would open up for some amount of arbitrage. But the amount of such value exchange would be directly proportional to the amount of usefulness of the new currency. E.g. if I said I would sell 10 grams of gold for 1 robem, someone might pucharse 1 robem for an amount of USD lower than what 10 grams of gold costs. And that would technically have 'lowered' the value of the USD since one person wanted to get rid of a small amount.

But it was not the creation of the currency itself that lead to this. It was the creation of new economic opportunity. You can create new crypto currencies all day and it wouldn't make a difference unless you also convinced people to use it.