Old stats or new I don't think Greece has a huge muslim population. First of all Syrian refugees are not citizens and they will never be included in the census. Moreover, European origin Muslims have a low fertility rate unlike South Asian and African muslims. Thirdly Greece is economically poor and no one from outside would immigrate into that nation.
What's that got to do with having a mosque ?
Let me put in a way you would understand, Christians form 0.4% of the Bangladeshi population, indeed we have more Buddhist like you then we have Christians... But yet we have dozens of churches in Bangladesh....
In fact that first church in modern day Bangladesh was built in 1601 and is still operational to this date...
So it matters little how big a community is, you need to provide them with a place of worship.
Are you telling me that Greece, a country with 2% Muslims, native Muslims btw of Turkish origin, can't built a mosque for them ? Forget refugees, Greece is bound to have Muslims as it borders Turkey a 83 million strong Muslim nation.
This is a nonsensical arguement, Greece is just sore at a history of being rolled over by Muslims and is now licking it's wounds anyway it can, including but not limited to punishing all Muslims by denying them a place to worship.
Even the only underground basement mosque was raided in Athens and shut down recently.