I seriously doubt it, there is almost certainly something else going on. Does the dropbox api even use udp at all? A udp flood has little to do with the size of a file transfer, and everything to do with the rate of udp packets per second. Generally to be identified as a "flood" your server would have to be doing something very poorly coded (best case) or downright malicious. Did you check where this udp traffic was being sent to (destination ip addresses/ports)? Did you compare the dates/times of the "flood" to when your scripts/jobs were running? Did you check your server for any suspicious activity or indications of compromise? A little bit of critical thinking can go a long way here.