It doesn't suffice if one component is non-blocking. All must be in order for the whole thing to be non-blocking. If just one thing blocks, everything blocks.
Even in Node.JS your application might still be blocking, even if Node.JS in itself is not: If you do a blocking filesystem or DB access (for whatever reason) it will still block.
Just as a PS: If something is blocking, it doesn't mean it's bad. So this is no argument for or against Node.JS. For some things you really need non-blocking applications and you should use Node.JS for that, but for most applications PHP is the better choice (due to bigger community support and integration.)