It would be easier to break, the greater the pressure differential between sides. My claim is breaking it would be easier. Not my fault he didn't pick the method that would best take advantage of the forces at play!
You weaken something under massive stress where it can no longer support that stress, and it will break!
I didn't choose the method

Just going along with the thread. Banging your soft worn down keys against the window isn't going to do much. In that scenario using a light soft object you are simply using blunt force to "bend" the glass to the point of shattering as you would with a fist, and that will be much harder if not impossible with water pressure on the outside.
Your best bet with minimal tools is sticking something in the edge seal and prying edge on as if you were trying to force the window down its tracks; tempered glass is extremely vulnerable at its edges. Tempered glass can bend quite a bit, but the slightest nick at the edge releases everything instantly. Though automotive glass has thick rolled edges to protect the glass for that very reason; furniture with ground and polished edges is much more susceptible to shatter.
Scratching the surface isn't sufficient; plenty of scratched up kid abused dining room tables, computer desks, coffee tables, desk mats and even hard rolling office chair mats that live through years of abuse, impacts, point loads, and daily surface scratches. But nick the edge during a move and BOOM.
Spring loaded center punch works great. You should be carrying one of these in your car anyway for people who hit your car in parking lots and don't have insurance and don't leave notes.