Yep. Almost all operating systems have a bufor that tell programs file was moved when it is still in the process. It makes perfect sense, it speed things up and extends the lifespan of the device.
You can flush that bufor manually with just the sync command or disable it for whole partition with -o sync option. Technically you should unmount drives before unplugging for safety anyway, but people are stupid or more important lazy and in my opinion for external devices mounting with sync really should be the default. Maybe some low-level developer would disagree.