Any language (even NodeJS) doesn't have much role in "scalability". Scalability consists of a lot of other things like server infrastructure, horizontal scaling, load balancers, routing, caching, database etc.

Big companies like Uber, Netlifx having millions of users are already using NodeJS as the main API-layer.

What did he exactly said? Maybe he meant NodeJS cant handle 10M concurrent connections from a single server.

PS: We use NodeJS at mfy.im and we're serving millions of requests without any issues :)

Scalability isn't just a factor of the language you chose. It is more dependent on how you design your system.