The spotters are in jail in Fujairah. So it seems likely they were taking pictures at Fujairah airport.
See this newsreport
Three Dutch spotters are in a Dubai jail for three days now being charged for espionage. They made photos of forbidden objects as it seems. There is no information on the place where they were arrested by it seems to be DBX.
DBX has always been a bit of a challenge. I know a couple of stories where people were taken to the policestation for questions. They were kept there for max 4 hours and were allowed to go.
Especially the area on the east side of the runway is tricky as you are in an isolated area where anyone can see you.
All the main dutch newssources are reporting (the same) news.