Why the Deutschland class was not a battlecruiser

Can the Deutschland class be considered battlecruisers because they were commerce raiders?

No; they were long-range heavy or armored cruisers whose vulnerability to other cruisers falls short of the battlecruiser's intended dominance.

The battlecruiser label does not fit, while armored cruiser is a more defensible comparison. The Deutschland class was a long-range commerce raider, but it was not designed to overpower the cruiser force likely to hunt it. Its concern about contemporary 8-inch-gun cruisers separates it from battlecruisers intended to dominate ships below the battle line. The pocket-battleship name was effective publicity rather than a reliable guide to design or mission.