In the video they said someone along the lines of, "we've deiced to do a pencil drawing and and not an art drawing, i'm quite confused by this, 'cause how is this going to work with computer drawn champions and an hand drawing, if you look when they're is a champ on the map it looks very odd and off, quite frankly it's just not going to work in my opinion useless Riot changes the look of EVERY CHAMP/SKIN.
there are more than 100 champions with at least one skin(Some with more then 7). If you were an illustrator at riot, you'd understand what kind of work that implies. they have to deliver changes in stages not all at once. When riot refers to a pencil drawing, I think they want to to notice other aspects of the game before the new map (watch the video for more info and you'll get what I'm saying)
Pencil drawing to me means something along the lines of a beta test. the kinks haven't been ironed out yet, and it is a rough version of what's to come. It must take a lot of effort to work at Riot, because there are so many people who use the product, so Riot tries its best to make everyone feel on board with whatever changes are incoming. Riot does this by having a public beta environment.
I'm pretty positive that what they meant by pencil drawing was the background. It looks morel like someone spent the time to draw their own illustration of what they think the area around the field of justice looks like. O and don't let 
kill you....
That's actually quite good that champions and the map look differently, bright colors are for champs and their abilities, it helps with clarifying the gameplay. And it's also logical, the Rift does not change much over the course of the game and so it's like an art object, hand drawn style.
