He spun the thing as the quickest way to lose height without over speeding
I'm not a glider pilot, I admit that, 'only flown them a few times (and really enjoyed it!). But I am rather experienced at intentional spin entries. For my experience, a spin can be entered from slow deceleration, which will take planning, patience and time, or, from an abrupt maneuver, which will generally see the required decay in speed as a gain in altitude first. Therefore, as a rapid evasive maneuver to lose altitude, a spin entry would not come to mind. Nose down and a sideslip would....