The second half of the tale
Although the tale Leo and Silver had told so far was amazing and beyond what they could have ever imagined, it didn't explain what Silver meant by her words, saying that Bryce wouldn't attack and how something bigger was on the horizon.
Little did they know that this was because it was only the first half of their story and there was still a lot to go from when they had returned.
It was explained further by Ham that when they had moved to the Familiar World they had also moved from the position they had entered as well. Although the Boneclaw could have gone back, and opened a portal up there time wasn't on their side.
If two more energy balls were to escape from their bodies, then it would possibly be life threatening. As such they had no choice but to go through the portal that had been created and hope for the best. The Vampire World was not exactly the smallest, so they could only rely on luck to end up somewhere near the Vampire settlement.