Greek territorial waters are 6 miles, so the rest are international. Territorial waters give the littoral state full control over air navigation in the airspace above, and partial control over shipping, although foreign ships (both civil and military) are normally guaranteed innocent passage through them.
So it is perfectly normal for a Turkish ship to be present in this area, even for communicative reasons of impression of Turkish public opinion.
Soon, Greece(as did in Ionian sea) will extend its territorial waters from 6 miles now to 12 miles from the South Crete coastline.