Sure, it's possible they have a net negative dollar flow because of investments. But that's a lot different than having a net negative dollar flow because they're importing oil.
https://atlas.media.mit.edu/en/profile/country/chn/
The net exports decreased to about 500B for 2018. I can't seem to find a dollar figure for 2018 oil but I've seen articles saying imports are up 10% by volume. So total petroleum imports are less than half of their net export amount. Meaning that they could triple their petroleum imports and still be a net exporter.
https://www.currenciesfx.com/index.php/eur-usd
So hundreds of billions of dollars a year is small relative to the volumes being traded.