War-time Diplomacy
Eren gulped nervously.
If he had the liberty to sweat in trepidation, he would have. If he had a way to disappear from the scene without anyone knowing, he would have done that in this instant as well.
Eren knew what Garos was talking about. He was the thief the Sage was looking for. Of course, the butcher wasn't aware that he was committing a "crime" at the time of committing it. He had just taken what he thought belonged to nobody.
The more he learned about spirit beasts from Nira Nightshade, the more he realized how fortuitous his encounter really was. He also doubted that Alephee knew an ideal environment had been created for the spirit beast's formation and growth. And that it could only be done by a Sage like Garos.
Alephee chose not to talk about a potential spirit beast owner at that time. This is because she thought Eren's cautious nature would have prevented him from messing with Sages.