I think the teleporting shyt is meh, but I get it. Gotta squeeze a lot of events into 13 episodes. Like somebody else said, euron could have just sent somebody else to deal with casterly rock. Look up a map of westeros and u see the Iron Islands and casterly rock are actually close neighbors, so euron could have sent a bird from kings landing to one of his generals on the islands to pull off the attack, cause there's no way he was gonna get there that fast.
The only thing that throws off that theory though is the fact they showed eurons ship, silence. If they would have just not shown it my theory would hold up but..
Anyway, loved seeing my man snow refuse to bow to Dany and still get his dragonglass. Soon Dany will be begging him for help and I can already hear her saying "if u help me ill help u beat the walkers and I'll marry u bae"