This is exactly correct. OP must have never made a bet before in his life, Vegas and sports bookies make money off the juice, or the cost of placing a bet. Betting 100 costs 110. YOU can PICK either side. They don't tell you which team to pick. The spread has absolutely NOTHING to do with the actual score of the game, they are giving the underdog enough points to entice a 50/50 even split on the bet so that when either team loses, they use the money lost by one side to pay the other and pocket THE JUICE. They are basically charging you to bet against the people who picked the other team.
Also to completely discount OP's theory, 7 points is exactly what was needed for the vikings to cover the spread that game with the wiffed tackle. The vikings chose not to kick the extra point, which let the saints cover, which they were doing prior to that play. The Vikings didn't know the spread but if they did, not kicking the XP was a big **** you to everyone who bet on them and Vegas.