It refers only to soldiers wearing BDUs and even then only in places which primarily sell alcohol or, if in a restaurant, the soldier is drinking only.
None of this would apply to having a drink on an airplane.
4. AR 670-1 PARAGRAPH 3-3A IS CHANGED TO READ: SOLDIERS MAY WEAR
BDUs ON DUTY WHEN PRESCRIBED BY THE COMMANDER. SOLDIERS MAY
WEAR BDUs OFF POST UNLESS PROHIBITED BY THE COMMANDER. THEY MAY
WEAR BDUs FOR COMMERCIAL TRAVEL, UNLESS OTHERWISE DIRECTED BY
THE COMMANDER. PERSONNEL MAY NOT WEAR BDUs IN ESTABLISHMENTS
THAT PRIMARILY SELL ALCOHOL. IF THE ESTABLISHMENT SELLS ALCOHOL
AND FOOD, SOLDIERS MAY NOTWEAR BDUs IF THEIR ACTIVITIES IN THE
ESTABLISHMENT CENTER ON DRINIKING ALCOHOL ONLY.