Just like the answer of Hannah, I also think that Oliver is not being ungrateful to Dodger and his gang. He is confused at the beginning, being in the package and not knowing what is happening. There is the fear that he is feeling that contributed to him being uneasy towards the group. It is a big difference to the warmth and love he felt from Jenny. This change of environment also contributes to the behavior of Oliver in wanting to go back to where he was rescued. Lastly, I think the way he was rescued, even though they have the good intention, was not clearly transmitted to Oliver, causing him not to be too thankful for the motive of the gang. In the end, he really just want to go back to Jenny, hence his actions.