Hi , I'm James DVM MRCVS and would like to help you with your question
There are some diseases which might effect both species but both would be showing the same symptoms towards that disease so if your Gerbil was sick , I would have expected you Hamster to suffer from the same symptoms.
In light of this , I find it hard to believe that your hamster is the cause of death of your Gerbil .
Gerbils are very sensitive animals , especially with regards to climate changes which might have had something to do with it but I can't be sure . The only way to find out would be to perform a post mortem exam on him .
Again , sorry to hear about you little friend , but I would not put the master as prim suspect .
If you wish to discuss the matter further , let me know and I shall be happy to help.
all the best