The Patriots had just intercepted the football and had the ball on the 1 yard line. Due to the field location, they couldn't just kneel the football; instead, they needed to buy some real estate to separate the line of scrimmage from the goal line.
The Seahawks defensive lineman Michael Bennett jumped into the neutral zone, whereupon offensive line captain Dan Connolly jumped up and drew the five yard penalty.
It was situational football and the Patriots knew exactly what they were going to do at a crucial point in the game. They knew they were going to draw someone offsides- and they knew Bennett had been hit for a league worst 12 penalties at the line of scrimmage (offsides, encroachment, neutral zone infraction).
Here's Belichick breaking it all down (go to 3:05):
"What's going to happen if the offense jumps offsides? Half the distance to the goal. How far is that? About this far. Ball's on the one yard line, half the distance to the goal, they get penalized two inches. So why not try to draw you guys offsides? It's the cheapest five yards they can get. That's the situation. They're backed up, you got to be ready for a hard cadence, [if you jump] that gets them off the goal line. If they miss it, what do they got to lose? Nothing. Two inches. They're on the one yard line anyway. Okay? Situations. Situations."
Brilliant, brilliant, brilliant, and always prepared.