It's not ideally signposted by any means, but interpreting it as having two alternate routes around the Railway Centre seems plausible to me. Looks like the "main" signposted route is the long loop to the South, past Didcot Parkway station. However, if you can handle riding North for 50 metres and sharing a road with some lorries, you'll discover some (older?) nationalcyclenetwork.org.uk - branded blue sticker-signs, mostly without numbers, that lead you via a much shorter route over a footbridge. Handy shortcut, not obvious on the ground, so I've added it to the route.

In other news, getting face pebbledashed repeatedly by clouds of tiny yet dense and impactful flies reminds me how little I like off-road cycle routes.