Why did someone in my server find a ton of drops?

I was playing TF2 and all the sudden someone found a lot of drops all at once:

How did he get these all at once?

Solution 1:

The person in question may have been inactive for a long period of time, so he did not open the window that shows his drops. His item drops will have accumulated if he was dying periodically due to idling. So he would have opened the window after being AFK and recieved all dropped items.

Solution 2:

All of the items dropped are achievement reward items.

This is a case where the person used SAM or a community server with the correct plugins, to unlock all of the achievements with item drops. They then joined your server and got the item notification which they acknowledged, showing the drops.