I would not say SD card being in during update is a guarantee of having an issue... But it is often put forward as a solution to update issues that the SD card be removed. And it seems to work. Coincidence or not? I've seen this scenario across many models according to posts in the forum. It gets put forward as a solution and the user comes back with, "Thanks, it worked."
When I first got my 1520.3 it came out of the box with Black. Cyan was waiting and ready. The OTA failed to install after download. I removed the SD card and went to a clean install via the (then named) Nokia Software Recovery Tool. That succeeded first try. Was it the memory card? Was it the OTA file. IDK. The problem is I changed two things. Which? Both?
It doesn't really hurt or take a huge amount of time to unmounts and remove the card... It can't hurt the process and seems to help many who are having update issues.