NATO would like to present a common front against Russian aggression, particularly with Putin seemingly likely to use such aggression to foster support for his regime during a serious economic downturn. To me, it's fully understandable that NATO and leaders of EU nations are concerned about Greek overtures with Russia.
While Greece may have taken a screwing from western bankers, etc., the fiscal management of their country, with or without European intervention, has been pretty abysmal. Tax evasion is a national pastime there and it's pretty damned difficult to balance the books when
6 in 10 pay no income taxes. The gap between what Greek taxpayers owed last year and what they paid was about a third of total tax revenue,
roughly the size of the country’s budget deficit.