They believed that this decision made was as a result of being the use of cryptocurrency as a means to engage into illegal financial activities such as scam and other fraudulent attempts by the people, you can read further from the links below and drop your opinion on this ban.
When almost all parts of Subsahara Africa are friendly with bitcoin, those North Africans which are Muslims against it. It got better over time but now Algeria is making things worse for their citizens because of their government self-centeredness. I will say the reason you stated above can be what their government said but the main reason they ban cryptocurrencies is because of their ignorance and their illiteracy part of themselves.
Yeah, you are right, Muslim see everything related to cryptocurrency especially Bitcoin to be sketchy and that every users using it are scammers, but that's not true actually.
Algeria should rethink about crypto especially Bitcoin, if they banning it, it will literally take them backwards, the most important thing is to regulate it distinctively.