Here's the data for the planet....
GJ 436b
There could be another reason for the deficit of methane....the presence of a catalyst in the atmosphere. Given it's density, if this planet doesn't have a well defined core (i.e. it's relatively well mixed in its interior), then that catalyst maybe Fe, in the form of small particles floating around in the atmosphere). I'd suggest they try and get both spectroscopic and albedo measurements done on this planet as soon as they can.