The author doesn't implicitly state this, only that his neighbor also has it. You're still failing to understand that a $50 SOHO router has a cheap transceiver and getting to your neighbors guest network is far more latent and prone to dropped packets and errors due to the distance. Also the embedded transceiver in the cable modem is competing with a lot of local RF from the cable modem.

Again, he's not doubling his bandwidth based on the above and a whole host of other reasons beyond these.

For those who try I'd say post true bandwitdh and latency test comparisons using multiple sessions that are shown using both links. Its actually pretty funny to me, having been in network engineering for well over a decade, that people are so passionate that they're sticking it to Comcast and "doubling" bandwidth with nothing to back it up. But, whatever floats your boat.