Yes, the PastBlocksMass is every 2 blocks. This was introduced from Spain Coin when the upgrade was made to Scrypt-N (as you can see in the code). The actual difficulty retarget should be every block.
Great job. This coin cannot be killed by a 51%
If a crypto has fast difficulty re-targets, it's difficulty to do a 51% attack, cause in the forked chain the difficulty will increase rapidly and will soon reach the target block times, the block time of the main chain will be the same, making a 51% attack impossible.
If the main chain's difficulty was high cause of the attacker's majority hashing power, it'll drop to sustain a block interval equal to the attacker's fork chain.
