No idea about the why of the light bleeding since this was a cube split into parts (normals pointing inside), but this may be explained in later lessons when actually rendering (i guess?).
The textures shown are from the same source he recommended in the video, the website is called textures.com, then the one i found some time ago is now called ambientcg.com and was previously known as cc0textures, the license for this last one is CC0 1.0, make sure to check their license page though.
Oh, also, at the bottom of the ambientcg website they have a link about how to make your own PBR materials and goes very in-depth if anyone reading this is interested in that!
Cheers! 