You are seeing all of the package updates from the date the Desperado ISO image was made, until yesterday -- several months of updates. Normally, if you update once per week or more often, you will see only a few packages -- maybe a couple dozen at most. Sometimes the updates actually reduce the amount of disk space used by the OS -- I saw that a couple days ago.
Yes, this is Debian Sid, where new software versions are frequently introduced, so you will see many more updates than you will in any distro based on Debian stable.
So just go ahead and accept this update, then you will need to reboot since there is a new kernel in the update, and then your system will be up to date.