Ti Ming Tan

Hello all experts, My first post in renotalk! Any idea what spots these could be on the drop ceiling in my new place? It's basically the whole drop ceiling - yard, kitchen, walkway, one toilet that has the spots Note: This unit I bought is unoccupied for about 1.5 years i.e. the owner took keys from developer but never moved in. ID and ceiling person happily declare "it is mold" and "suggest" me to replace the whole drop ceiling (obviously need to pay).