That is fine!
I am still wondering. Assuming that your conclusion that /dev/sdb is indeed the mass-storage device you want to tackle.
You used /dev/sdb in your first CODE snippet. dd did NOT complain that it does not exist, but did what you asked for (though not what you wanted to do).
Then you umount /dev/sdb1. That is a bit late (better not overwrite a file system that is still mounted)., but again, no protest.
Then you use fdisk on that device and fdisk says there is no device file with that name???
Did you remove it (you say it connects through USB, thus I assume it is possible to remove it while the system is running), or what happened? I can not really understand this.