To be fair, Greece acted decisively and swiftly, so im not that surprised.
I have a friend who lives in Athens who I visited in mid March. I started keeping an eye on what was happening there in the run up and they closed all of their schools in early
March before they had even hit 50 cases.
On my second day there the country went into full lock down. It went from bars and restaurants being open to a ghost town over night and everyone adjusted to it really well. People were queuing and socially distancing at shops right away.
Their numbers were always behind ours (for various reasons) but they acted much earlier and more rigorously. On the day I left the rules changed again and anyone entering the country had to quarantine for two weeks.
It was quite jarring arriving home and seeing life going on as usual here given our numbers were worse and our population density more conducive to spreading disease more quickly. I essentially quarantined myself for two weeks when I arrived back because the landscape had changed so much in the space of a week. I felt Greece had been a much safer place to be than here but thought I should take precautions given I'd passed through an airport.
Anyway tl:dr Greece's numbers are impressive but not surprising as they took it really seriously much earlier than us (plus other factors too such as population size/density)