Ok, a couple of things:
1. Just because dinosaurs could walk from Eurasia to North America, does not mean they couldn't have built boats. This is a nonsensical point killabee, so stop making it.
2. However, as Dogplatter has pointed out, the fossil record supports the idea of dinosaurs travelling by boats. Though they could still have walked across continents, the fossil record does not support this, as the fossils have been located in places which suggest ocean travel, and which do not suggest coastal migration.
Now, the dinosaur fossil record is notoriously weak, so there may yet be fossils awaiting us on the eastern Eurasian and western American coastlines which indicate that dinosaurs travelled by foot along these coasts to travel from one continent to another. But the evidence we have indicates ocean travel.