I think they used "mainland" here, so that it is differentiated from something like Hong Kong. And in this case, that differentiation actually matters and helps

I think they used "mainland" here, so that it is differentiated from something like Hong Kong. And in this case, that differentiation actually matters and helps the context. Tl;dr: the parent comment didn't use "mainland" to imply that Taiwan is a part of China. They used it to say "contacted by recruiters from Mainland China [as opposed to recruiters from HK]"