Yeah many many ways to get sea dino's beached.
Some sort of predator grabbing at them and and dragging them on shore
Corpse naturally washing to shore
Storms beaching them
Swim to far into shallows while hunting and get beached
Drought trapping and subsequently beaching the dino
I mean if modern day Whales etc. can swim into central london and get beached I'm sure a dino could do it.