As I wrote in a comment above, I also believe that it is unrealistic for many reasons.
You could also think about it from a technical point of view. How would you program the evaluation function of that website (No idea whether that code is public or not.)?
The best you could do I believe is that you have each of the ten positions analyzed by an engine. Then you match the entered moves to the engine evaluation.
In the simplest case you just accept the best possible move and assign something like 200 ELO points to each correct answer (so as to cover roughly 2000 ELO point range from beginner level to World Champion). So you have a huge error just from the method used (not including all the other factors I mentioned in the comment).
If you want to do it a bit more fancy you could also accept second, third, etc. best moves and give ELO points for them, perhaps weighted (with an arbitrary weight). As you can see, all of this seems a bit random.
In summary a few points not related to the technical difficulties mentioned above:
The ELO system is made to measure the relative strength of players, not the absolute strength (which might not even exist) as this site is trying to achieve. So by design, the ELO rating only tells you how strong you are relative to all other ELO rated players, not how strong you are overall.
Players might have the same rating but completely different strength and weaknesses. How do you expect to measure all the different factors with just 10 puzzles?