In electronics terms, sink means a device which consumes current. The opposite is aptly named source. So a source supplies a sink.

The 100W 20V USB-C power standard requires a negotiation protocol to tell a source what the sink requires. This is to ensure a source is not overloaded or a sink fed the wrong voltage. So this article explains how the author used an off the shelf USB-C power chip to talk to a standard USB-C power source and request enough power to charge their laptop (the sink).

No this is a device that is powered by a USB-C charger and outputs whatever voltage/current you want (if it is possible).

So in this case he made an adaptor that lets him charge his lenovo laptop (traditional DC charger) with USB-C.