Track frame... I'l bet it's got really short chainstays. The split in the seat tube is to allow the rear tire to slip between. Sort of a modern-day Rigi. The Rigi, BTW, was the quickest handing bike I've ever ridden. Head angle around 78 degrees, chainstays around 13 inches, wheelbase under 37, IIRC. Any roughness in your pedal stroke would make the bike hunt from side to side in time with your pedalling. They made both road and track frames.
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