NC State vs. Florida State

[GPC2]

I'm not totally clear on college mechanics, but this couldn't possibly have been the proper mechanic. An NC State running back broke a long run (beyond the first down line) and at the end of the run he was tackled and the ball came out. It appeared to me that he was down first, but the Linejudge never blew the whistle, so I thought maybe it was a fumble.

Following the fumble(?) the Linejudge just stood there as players scrambled for the loose ball. After a few seconds, a Florida State defender recovered the ball. At this time the Linejudge blew his whistle, stopped the clock and pointed to the ground and gave the first down signal for NC State.

Is that the proper mechanic, or should the Linejudge have immediately signalled that the runner was down? Seems like a dumb question to me, but maybe I truly don't understand the proper mechanics.