The reason for revoking the citizenship was undermining Moldova's legitimacy by calling for the reunification of Moldova with Romania. Moldova's newly elected president is known for his anti-Western and pro-Russian views. They did have to find some other pretext to declare that the guy's Moldovan citizenship was obtained illegally, and they did find some minor procedural irregularities apparently.
Moldovans generally can get Romanian citizenship because Moldova used to be part of Romania and the current generation's grandparents were stripped of their Romanian citizenship by force when Moldova was annexed by the Soviet Union after the WWII. Likewise, Romanians whose grandparents were born in what is currently Moldova while it was still Romania can claim Moldovan passports.