Yes, this is true, especially in a regional sense. Easterly wind anomalies basically slow the Earth down, causing +AAM to be transferred from the solid Earth to the air. In the case of mountain ranges, a surface low anomaly to the west of it (and high to the east) will cause a net easterly over the mountain range and slow the Earth even further than if it were just the mountain range alone. So a negative frictional torque and a positive mountain torque contribute to regional +AAM anomalies. The correlation with the AO is actually not so clear-cut; and, in fact, the +MT showed a +AO tendency in some research. This is because the +MT increases the net Mid Latitude westerlies over time, intensifying the jet and PV. There exists an internal AAM cycle across the Mid Latitudes that occasionally is independent of the tropical source to mid latitude sink cycle we are accustomed to (tropical forcing). The internal cycle is simply mid latitude (mainly over the ocean) frictional sinks eating the momentum produced by the mountains in the same latitude-belt. So, not all +MT events are created equal and not all will occur with, and/or lead to, a +GLAAM/meridional flow. I hope this helped.