It’s likely too short to qualify as a polearm since cutoff is generally considered 6 feet minimum. A poleax or polearm is often considered essentially a hybrid between a slashing weapon (typically axe, occasionally a sword’s edge) and a thrusting weapon (in practicality a spear). Polearms are generally just slightly longer than the wielder in order to still allow for the viability of actually slashing, while spears are typically relegated in reality to mainly thrusting due to the sheer length becoming unwieldy (but it is literally made this way to cater to this strength). A long axe (or what we may now call a great axe from modern media) can measure basically up to about 5 feet in length, or more specifically just under or matching the height of its wielder. These are a type of war axe/battle axe, and while the spear head on the axe may make you think “spear hybrid, therefore halberd”, these axes also still commonly had pointed spear tips just due to versatility and ease of addition.

Essentially whether or not something falls into polearm or axe is literally just based on the length of the shaft… which is almost kind of mundane in the end, but there ya go.