It might have been on loan, but described as a gift as there’s limited numbers they loan out.

Part of the reasoning for the loan system is that there’s a limited number, and the terms of the loan allows China to take them back in the event the zoo fails to care for them appropriately, which happens with depressing regularity.

They are given as a loan. The Wikipedia page about Panda diplomacy someone else linked is quite interesting and explains it all.

Gifting the temporary use of the panda