Marg, you are correct that it should be ‘ Ils appellent leur chien. ‘ for ‘They are calling their dog.’ 

The reflexive is used when the ‘subject’ performs the action on ‘itself’ - that is the verb’s subject and object are the same, which is not the case in the sentence under question.

If you think there is an error in the quiz/question, you should use ‘report it’ from there directly for review. 

https://www.lawlessfrench.com/grammar/reflexive-pronouns/

 https://french.kwiziq.com/revision/glossary/verb-types/reflexive-verbs 

https://www.lawlessfrench.com/grammar/reflexive-verbs/