This is either a state actor operating under a fake name or it deserves to be one.

The perpetrator, "Jia Tan," let's assume has last name 陈. In Mandarin, this is pronounced as Chen, in Hong Kong as Chan, while in Minnan this is pronounced as Tan. Minnan is prevalent in Taiwan, Singapore, Malaysia, Indonesia, and other southeast Asian countries as well as in parts of Fujian, China (where it originated).

A common feature of early Chinese expat communities was that they were overwhelmingly from Guangdong (think Gold Rush era). However, more recently, there's been a massive wave of Taiwan and Hong Kong emigration... The relevant takeaway here is that Tan is much more common of a pronunciation in expat communities than it is in China.

Of course, they could also have the last name 谭, but that's a good bit rarer. 陈 is the most common Chinese surname overseas and the 5th most common in China, while 谭 is something like 54th most common in China. Odds are high that, if this was a persona constructed by a state actor, it did not come from China but from an overseas actor for which Tan is a more common romanization.