One criteria could be dry lease (put it to the lessee) vs. wet lease (put it under the lessor). Another one simply the color scheme or you wait for Aurbus OD. MSN 265 seems to a be dry lease, operated by Qatar.
We recently had an unconclusive discussion on this topic. I like Sciing's criteria. In this case, both the paint scheme and the nature of the lease agreement (dry and short-term) dictate that the frame be considered as part of the LATAM fleet.
If we take this criteria, we would have to count all leased aircraft at the leasing companies, not the airlines flying it.
This frame is leased to Qatar, it is on a Qatari registration, it is flown by Qatari personal, the only argument to count it with Latam would be the length of the lease.
Regarding the form of the lease, a wet lease counted at the lessor a dry lease counted at the lessee would be logical.