Dollars to doughnuts this is collecting keypress-cadence data for fooling anti-automation algorithms with natural typing speeds.

Mm, doughnuts. I'll take the flip side of that bet, since I don't think capturing the typing cadence for individual words would be all that helpful. I'd bet the typing cadences here are distinguishable from the cadence of normal English text (as might be collected by a malicious browser extension which vacuums up keystroke data on popular UGC sites).