How exactly did you decide it might even remotely be a good idea to take a horse that has never jumped and expect him to jump 2 feet?
You're really lucky he plowed through the jump instead of dumping your sorry rear.
Randomly jumping a fence is NOT the same as being trained to properly jump over a jump. Any horse can jump. One of the pastures where I board has an irrigation ditch in it, Every single horse has at some point jumped over that ditch to get to the grass on the other side. 8 horses and I would only consider pointing ONE of them at a jump and that's because he's a hunter/jumper pony and trained to jump! The rest give that ditch the evil eye and haul ass over it. Even the Warmblood who was bred to be a jumper! The breeding is there, the capability is there (holy crap can this horse move) but the knowledge is not as she is still to young to be jumping.