Actually if you go back the last few drafts, there were a few top ranked prospect that actually fell in the draft because teams were more interested in selected a player that their team scouts thought were better than the general scout rankings.
2011 - Adam Larsson was thought to be good enough for 1st OV - picked 4th OV
2012 - Filiip Forsberg was seen as a top 5 pick but ended up 11th because teams were high on the defenseman
2013 - Seth Jones like Larsson was thought to be good enough as a 1st OV and fell to 4
2014 - William Nylander was seen as the best European and another kid that was seen a top 3-5 player because of his pure skill compared to the other players but fell to 8th.
2015 - Noah Hanifin was good enough to be a top 3 but Arizona and Toronto wanted scoring over defense so he dropped to 5.
Every team has ideas of what type of players they want to build their team with which is why it seems every year draft day gets crazy with trades and teams surprising people with their picks.
Even with the player Tkachuk has on his line, the amount of the points the kid is producing is unbelievable and if his team goes to the Memorial Cup and wins it, he will be a huge part as to why. It would be stupid for Columbus not to take a hard look at him (not to mention he's also an American). Also, with Edmonton being rumoured to selected a defenseman for need, there is a chance that Puljujarvi could fall to 5.