This could be "at his house" or "at your house".
Can be confusing
Could you also say my friend ate at your house?
I wrote 'my friend ate at your house' and it was accepted.
"My friend has eaten at house"
= Meu amigo comeu em casa.
I know, but it said "My friend has eaten at house" would have been a correct answer which just sounds weird and plain wrong in English.