I am not sure if this is correct info since its off a an internet care guid I just found but I thought I read on this care sheet that Dwarf
Clawed frogs usually need up to 1 gallon per frog so if you had it in a 5 gallon you could have easily kept others in there I would assume.
It also recommends that you can keep fish with them but usually ones that are not that much bigger then the frog or more "peaceful fish"
if you want to take a look at the site this is it:
Dwarf Clawed Frogs - African Dwarf Clawed Frogs
Swirly, Squashy, Squishy, Spot, Star, Slash and Rocky
Indy and Myfanwy 
Tilly, Emil, Sonny and Smudge
