They are aiming to please power-users, some of which might be pleased to know which stack is used.
In that case they failed horribly, knowing what a security nightmare NPM modules are and having that embedded in my browser is 110% turning me off from ever wanting to install Vivaldi on anything that's not securely sandboxed away from the world at large.
Yea, its alot quicker to develop and experiment with new features.