He said that it's not any more haram than fiat. He believes on gold and silver are halal since it’s the only legislated form of money in the Sunnah.
Discussion
'legislated' lol if you read the books of sharia economics you will find the majority say that anything can be used as a currency (as long as they possess some varying characteristics).
Ibn tayymiyyahs expertise is economics, read what he says about shariah currencies.