Help feces smearing at almost 6

We adopted our son G from the state.  He has been with us since he was 4 months.  However he had a VERY traumatic start and both of his natural parents have signifigant Mental health issues..  He has been developing well.  However he has some vision and speech/motor issues.  He is now in Kindergarten and I received a call from his teacher.  The last 3 days someone has thown wet tissue with feces on it on the walls. The teacher walked in the bathroom and he was pooping over the trash can. She then figured out that it was G who was doing this.
The OT feels this is normal for a child who has anxiety issues.  He will be six in 2 weeks and is still very anxious about new environments.  But I have heard that children who smear poop have severe emotional issues.  What does someone think?  He has NEVER done something like this before.  Do you think it is the start to something more serious?  I asked G and he said he did not know why he did that..
Thanks,
G's mom