You can always call public methods from other contracts regardless what construct you use. The library construct is a Solidity implementation detail but you can

You can always call public methods from other contracts regardless what construct you use. The library construct is a Solidity implementation detail but you can also use normal contracts, like they did in this case. So far, it really looks like almost a criminal sloppy refactoring of the official multi sig contract from the EF that has been extensively audited.