The inhuman treatment of the Demis weighed heavily on his heart, but Arthur had a mission to finish. So, as he stood on the edge of the forest, he used his detection rune to find any traces of the hydra's child.
There were none.
Arthur sighed and walked into the forest, his eyes looking for any clues he could find. Just because his detection didn't find anything, it didn't mean that the soldier was lying; no one could lie to his art.
More than one possibility could explain why he couldn't find anything in the forest, and that was a counter-ability that prevented him from seeing anything. For example:
"Larza's isolation ability or the ender's powers," Arthur muttered as he looked through the trails for anything, but there was none.