In nearly all cars with both transmissions offered, this is true. See my post below.
If the engine is identical, the manual will usually get better mpgs, especially city mpgs.
I went from a 2.2L VTEC Honda automatic to a 2.3L Mazda manual & saw city mpgs go from 18 mpg to 24 mpg even though the new engine has a slightly larger displacement. Similar vehicle weight, btw. Its mostly the torque converter, as I never broke 20 mpg city in any of my 4-cyl autos but now both my 2.3L manuals do much better than that.

"Author" David Sirota hasn't a clue (I guess subject research is no longer a requirement to be a jounalist, who knew!?)
Generally, there are 3 transmission types a normal driver may encounter - manual tranmissions, torque converter automatics, and new dual-clutch automated manuals. Automatics have a torque converter. Consider this: When the vehicle is stopped in drive but the engine is running, the engine doesn't stall. When accelerating, in certain lower gears and at low speeds, the converter is slipping just like it does at a stop, until lockup occurs at cruising speed. This slippage is the reason lockup torque converters were developed in the 90s, and until lockup occurs, not all engine power is transferred, resulting in lower mpgs.