Surveyors don't usually dig with a pick in the road for a half an hour. It is good enough to make that distinction. What isn't mentioned in the report is that it is followed up by ground forces (to disarm any remaining bombs) which likely confirmed the activity.
If there's a utility break in a line on a road, it is very typical to have a crew of 2 or 3 men come in and dig it up, with ancillary surveying/measuring equipment, pipes, etc. near the site. Believe it or not, I have seen this with my own eyes. Of course over here they use power equipment too, but in Iraq that is probably not so available, it would more likely be done manually.
It would be possible to mistake this actvity for an IED crew. And, as others have helpfully pointed out, the predator has the ability to make that distinction. You my friend, do not.