First and foremost, probably the most impactful thing on it is personal preference and learned behavior, but make no mistake, when engaging there is a drastic difference in the two.
Coming out of a 3 point stance, your body angle to the opposition is always lower, watch the next game for the offensive lineman, note how his shoulders are upright and his stance is higher. If you can jump out of the stance, you have the leverage point, it makes it harder for the lineman to center his first contact on your mid body and naturally have the edges of the lineman to attack.
Also, the technique for rushing the passer are different between the two. Playing DE, your pass rush moves are more focused on leverage, hand "fighting" and close contact rips, swims, clubs and bull rushes.
Playing Linebacker, you are either setting the blocker up a yard or two away for your move or you are beating him on angle, quickness and speed.
Shooting from a two point stance you have to be more flexible in the hips, you have to avoid the blocker getting under your chest region (where Kampman is currently struggling) and taking away not only leverage but your lower body strength. It also allows the blocker to square up more and takes away some elements of quickness off the snap that Kampman had verses the lineman.
DD80 hit the other point, playing outside backer your "reads" on a play are much deeper than DE.. it takes some getting used to going through your responsibilities, diagnosing the play and then engaging effectively.
DE.. you are engaging much quicker then adjusting.
It is a progression to make the move, in some areas I think Kampman is further along than I thought.. basically dropping into coverage and staying with people.. but where I didn't expect that transition issues is here in engagement.. it will come more naturally as the season progresses, but will he ever have the same explosiveness off the snap?
I think he will gain some of it back, but not the same as he won with the close contact hand fighting and getting under the outside shoulder of the tackle..
"The oranges are dry; the apples are mealy; and the papayas... I don't know what's going on with the papayas!"