Emil no it's not. It's just his front-end framework, a "Package of small stand-alone components without dependencies". It's like jQuery and I get the feeling that Mev advertises it just the way jQuery once was advertised :D
Also the polyfills are quite incomplete feature-wise, which stems from the fact that it's not the focus of the project (and shouldn't be)
It contains everything you need to polyfill in ES6 which basically is only Promise and fetch, however, it has more like <template> support, yet, it might not contain everything, since I don't know what polyfills are you talking about and what do you need.
Array.prototype.reduce/map/filter are not ES6 and works even in IE9.
Mev-Rael take a look at the list of core-js to understand what stuff should be polyfilled. It is quite complete and you can see that it's not a trivial list of two or three things. For more details, you should compare the actual standards.
While IE11 might already be able to handle quite a lot, it is very annoying to find out later on that the polyfills used do not provide certain features, which leads to importing more and more libraries of varying quality.