yeah i'm pretty sure it jumped timing cause when i check the cam gears after it blew up the exhaust cam gear mark was facing the fire wall
No, this is not what happened. When you jump time enough to bang a valve, you bang all of them in all the cylinders. However, when you stave some valves into a piston, it's not uncommon to jump time between the increase in force between cam and crank and the engine loading/unloading as this happens.
The most likely answer is either simple mechanical failure of an OEM part taken beyond it's limits - whether you were cruising or not at the moment of failure has exactly jack and shit to do with what the valve has been through and any metal fatigue it's undergone. The other alternative, very likely, is that the head had a bent valve at some point that cracked a guide. Valve gets replaced, guide is still fucked up and the replacement valve hangs open and fucks some shit up.