It is because your script has wrong logic, you are getting of usernames but you are running same command for all users. Therefore, for first user it is already deleting the "*.app" file, and for all others it would return "No such file or directory" as item is already being delete. You do not need logged in user.
For better script you can use below
#!/bin/bash
# List of user accounts
ListofUsers=$(dscl . ls /Users | grep -v '_' | grep -v 'root'| grep -v 'daemon' | grep -v 'nobody' | grep -v 'localadmin')
fileExt="*.app"
for trash in $ListofUsers
do
# Delete app files from the currect user's trash
rm -R /Users/${trash}/.Trash/${fileExt}
# For logs or viewing progress--shows when the users trash has been emptied
echo -e "${fileExt} files removed from Trash for: ${trash}"
done
However, you will still receive an "No such file or directory" for any user that does not have *.app
