Hindus are supplying muslims with weapons?
Do I have this right?
Sort of like American capitalists providing Russian communists with oil, food, trucks and weaponry during WWII. Believe it or not, India attacked Pakistan in Bangladesh's (East Pakistan, a majority Muslim region of Pakistan, at the time) behalf and provided Bangladesh with weaponry during its successful secession effort from Pakistan.
Afghanistan is an enemy of Pakistan. Around a quarter of Pakistani territory is filled with ethnic Pashtuns. This was land carved off of the Kingdom of Afghanistan by the English back in the days of the British Raj. Pakistan and in particular the ISI have been working since the days of the Afghan civil war to keep that nation fractious and divided, in order to try and prevent Afghan revanchism. Indian support for Afghanistan is an indirect way to threaten Pakistan.