I think it is wrong to call bitcoin a "private" currency.
On the contrary, imo bitcoin is much more of a public currency that any national currency is.
Bitcoin is not a private currency but using of bitcoin is private for sure. Since its anonymous we can send or receive the a lot of money without giving any data or identity. Bitcoin is a public currency even AtMs are build in some countries many hostel schools are accepting it there's no chance of calling bitcoins as a private currency. Maybe you're calling it private because they're not exist physically but its internet currency and everyone is welcome to use it
bitcoin can also be called private currency because if we have invested in the world of bitcoin we can get a lot of benefits that we can use as we please. so it's the same as personal money.