Extra Minifigure in NinjaGO Set!

Today something unbelievable happened to me. I bought today NinjaGO sets 70756 Dojo Showdown together with 70753 Lawa Falls .According to Brickset and many other sources both sets should normally include the same Anacondrai character Sleven. But I realised that the 70756 Dojo Showdown set has pictured other than Sleven which has a torso printing with 2 snakes on it. I searched for the names for the characters and found pictures for the character as seen below.


NinjaGO Anacondrai character called Chope which has one large snake symbol on its torso. When you look closely you can see that Chope is pictured on the box of set 70756.


Besides the main picture in front of the box, also Chope is pictured on top of the box. I got excited when I found this mistake and opened the box. Than I realised that the Instruction Manual pictured the correct picture of Sleven


Then I see that both minifigures are suprisingly included in the box. They both came out from the original part bag. 


I'm buying and opening LEGO sets for nearly 25 years and I have never seen an extra minifigure in a box. I think that this minifigure is included deliberately because of a possible printing mistake. Either the box or the instructions manual was misprinted and LEGO company decided to include both figure before getting any complaints about the mistake. I searched the internet for this incident and couldn't found any info about it. Either this extra minifigure mistake only happened to me or the early released sets are released with only one minifigure and now they include one extra minifigure.