PrhinesI think someone read the Gamepedia page for this and thought M13 (Core Set 2013) was MM13 (Modern Masters 2013) - https://mtg.gamepedia.com/Magic_2014/Deck_Builder%27s_Toolkit . Also, MM13 came out only one month before M14 - so yeah, no way they were packing in MM13 that quick.
Anything else I've found agrees with the above - cards and packs are from M13 and RTR block (includes GTC, and DGM).