Scientists 3D print a robotic hand with human-like bones and tendons

This… just isn’t true. The robot movements can be incredibly fluid even with stiff structural members. A lot can be said about Boston Dynamics’ robots but not that their movements look stiff.
Some robots actually move in awkward, rigid way but in that case it’s down to the power system and control. For example, most industrial robots use either non-backdrivable drives (harmonic, cycloidal) or very large gear reduction ratios. Even if such drive is reversible, turning the robot arm requires spinning up the motor to very high speeds, which makes the joint non-compliant, or “stiff”.
It doesn’t necessarily take bones and tendons to fix the issue – much less soft ones. The first step is to use some kind of direct drive (linear or rotary) or at least one with substantially reduced inertia. Boston Dynamics robots use hydraulics and pneumatics to that end. This research doesn’t seem to address the drive or control issue at all.