They mean decoding at the level of extracting a signal & correcting errors in it from being sent across a wire, fiber, or broadcast. This is not the cracking encryption meaning of decoding.

The terms "coding" and "decoding" here are very specific terms of art, as it turns out. It's a confusing headline even for a general programmer audience.

China's great firewall has been using statistical analysis to kill connections that it suspects to be unauthorized encrypted channels.