Since the retirement of the US Space Transportation System (aka space shuttle) in 2011, the only crewed transportation to ISS has been in Russian-operated Soyuz spacecraft -- even for American astronauts.
Since then, uncrewed resupply ships to ISS of several types (Dragon, Cygnus, HTV, Progress, ATV) have flown regularly, a few times a year.
The Space Station has two distinct halves, the Russian Operating Segment (ROS), and the US Operating Segement (USOS).
Here is a picture I love of when the ISS had 6 vehicles attached all at once.
The ROS has 4 docking ports, that have accepted:
Soyuz (Manned crew)
Progress (Cargo, unmanned)
ATV (European Cargo vehicle unmanned) - retired
The USOS has ...
Semi answer because I think you misread a critical part of that quote:
I was a little surprised - I was under the impression that this happened much more frequently. E.g. ~ quarterly.
What exactly is your "this" here? Is it Spacecraft docking to the ISS (which I got the first read as well)? That happens about quarterly indeed. However, that is not what ...