What’s the difference in saying someone had a special season and saying someone had a elite season?
Elite means you're in the company of those who played at the highest level. In this case, it would mean the player you are referring was alongside other high level players that season.
Special would have to mean it is unique or unusual in some aspect. It was not. There are MANY rookie RBs that averaged similar to what Elliott did his rookie season. There was nothing about his season that was special. Let's use the very player you brought up randomly in the discussion
Saquan Barkley rushed for 1,307 yards on 261 attempts and 5.0ypc. If he had a similar amount of carries to what Zeke got, he would have similar results to Zeke. If anything, Barkley has more in his favor since he had 700 yards receiving. But let's go further into this.
Barry Sanders - 280 carries, 1, 470 yards
Mike Anderson - 297 carries, 1,487 yards
Adrian Peterson - 238 carries, 1,341 yards
Clinton Portis - 273 carries 1,508 yards
Jerome Bettis - 294 carries, 1,429 yards
Adrian Peterson's rookie season there is closer to being special, but he missed two games. He was averaging 5.6 yards on the ground and had 12 TDs on 238 carries. For the amount of carries that Zeke got and the line that he was behind, what he accomplished in 2016 is not special. It was a great season and he was among the elites, but not special. There is an RB every other season that averages around the same to what we see Zeke did as a rookie. Hell I'm not even sure why "rookie" even matters? We aren't talking QBs here. RBs adjust to the NFL easier than most other positions.