No, he didn’t say it needs more users to port it, just to support it. Support means more than getting it working, it means testing and customer support if there are issues, which means training testers and support people.
The extra load here would be much lower if it was a single player game, but because it’s MP, they need to know how exploitable it is by cheaters, and perhaps patch some vulnerabilities out.
It’s a lot more than flipping a switch, but it’s also something Epic could totally handle. He’s not lying, he’s just content to milk his cash cow as long as he expects to not lose too many customers by not supporting Linux.