This page states that:

Note: This will install an old version of Arduino, and may not support some of the newer boards. You can not download a newer version from the website, because there is no ARM version.

I'm not sure which version it installs by default, but it's older than 1.6.14, because it doesn't have the fix described here yet.

However, there is an ARM version available on the website. I have downloaded it using wget https://downloads.arduino.cc/arduino-1.8.5-linuxarm.tar.xz, and it works for verifying and uploading from a headless OS.

Can the apt package for raspbian be updated to a newer version?