TLDR: COPD is not the true cause, but it is an underlying condition that predisposes to SSP (the true cause is rupture of alveolar blebs).
Necessary clarification. UWorld Step 2 - 4520 uses this language exactly. This is because the true cause, echoed by UWorld, is not the COPD itself, but "chronic destruction of alveolar sacs leading to the formation of large alveolar blebs, which can eventually rupture and leak air into the pleural space." This is why, in the "educational objective" at the end of the UWorld explanation, it states that "Secondary spontaneous pneumothorax should be suspected in patients with UNDERLYING lung disease presenting with rapid worsening of respiratory symptoms. RUPTURE OF ALVEOLAR BLEBS IS THE MOST COMMON CAUSE in patients with chronic obstructive lung disease."