even if the other tank needs filling/cycling... (did he throw away the filter media? you might be able to salvage some of the bacteria!)
you need to remedy this ASAP. Even moving the frog to the uncycled tank and doing multiple water changes is better than leaving them together.

Also, are these new fish? If so then he might also have just introduced disease in with your frog. The mollies will probably be picked off at night as they hover close to the bottom trying to sleep. The paradise fish is just a risk all around.

Even moving the frog to the temporary tank is better than nothing. The fish should stay in the cycled tank for now because fish breathe the water, frogs don't, so you have to balance each of their needs with the situation.