Incorrect, to compare the dealer's discount on the used car you need to calculate the price of the new car. The gap between the used car price and new car price is your discount. Lets break things out and spoon feed the details:
New car sticker w fees: $10,000
Dealer markup and negotiated discount: ($1,000)
Dealer cash incentive: ($4,200)
Price for new car: $4,800
Used car sticker w fees: $4,200 (that's a $5,800 discount off the new sticker price, because $10,000 minus $5,800 is $4,200)
The difference is $600. The dealer is offering a $600 discount on a used car with 6.5k km, not $5,800. Its equal to a whopping $0.09/km discount.