If you check TeamManager.lua, you'll notice that the TeamManager variable itself is declared in a file local scope.
Lua Code:
local TeamManager = PetBattleTeams:NewModule("TeamManager")
You can access PetBattleTeams and probably use its function:
Lua Code:
PetBattleTeams:GetModule("TeamManager")
You can then access GetNumTeams from there, like so:
Lua Code:
local TeamManager = PetBattleTeams:GetModule("TeamManager")
local numTeams = TeamManager:GetNumTeams()