Correct me if I am wrong, but isn't the open interest figure BOTH long and short for both calls and puts? So if someone is short on a call, which is bearish, wouldn't that also show up as +1 in the call open interest? OI volume alone isn't that great of an indicator, you should incorporate the Bid/Ask vs. contract price to see if the volume is more bullish rather than bearish.
Please allow me clarify. While yes, someone must sell the call option in order for the other to buy it, the real value is in the ratio of puts to calls. Since 80%+ of all options expire worthless, that is the telling comparison.
To your point though, the option premium is also a factor, and with the call option (at the money) running at about 15%, that is another very bullish sentiment.