Can just anyone change the accounts and total supply?

Question

In fungible token:

pub struct FungibleToken {
    /// sha256(AccountID) -> Account details.
    pub accounts: UnorderedMap<Vec<u8>, Account>,

    /// Total supply of the all token.
    pub total_supply: Balance,
}

https://github.com/near-examples/FT/blob/master/contracts/rust/src/lib.rs

accounts and total supply is marked public, can't just anyone is able to change the accounts and total_supply

Does the blockchain chain only allows to access functions? But I am able to change the variables in tests.