As @jikolp quoted it seems that you misunderstood the statement متفق عليه only means that both al-Bukhari and Muslim have quoted a hadith in their sahih. As both of them has his own definition on what he calls sahih. And this doesn't exclude that the same hadith with the same matn (content)is quoted in any other hadith collection! 

As you see this has nothing to do with tawator!

**Condition of al-Bukhari, Muslim the two sheikhs**

Al-Bukhari and Muslim both had a number of scholars (narrator chains) whom they trusted and some of them are common for both of them and some only trusted by Muslim or only by al-Bukhari!
Now any hadith quoted as [متفق عليه][1] or رواه الشيخان would also be quoted to be sahih according the conditions of both al-Bukhari and Muslim (according to the condition(s) of the two sheikhs) على شرط الشيخين.
But for example if a scholar like al-Hakim who wrote his mustadrak as an expansion for both sahih according either the conditions of al Bukhari على شرط البخاري this my mean the narrator chain could be found in Sahih al-Bukhari or  على شرط مسلم this my mean the narrator chain could be found in Sahih Muslim or على شرط الشيخين which is explained above: then this would mean that the mentioned hadith is not in any of the two books but the rawys have been quoted in the Sahih books but either one or both of them have not quoted the hadith!

**Rawahu a-Sheikhan رواه الشيخان vs Mutafaq 'alaih متفق عليه**

The difference between متفق عليه and رواه الشيخان generally is as follows:

 - متفق عليه: means the hadith is mentioned in both sahih books with the same matn (content) and narrated by the same sahabi!
 - رواه الشيخان: means the hadith is mentioned in both sahih books with the same matn (content) but narrated by different sahabis!

But some scholars seem to have their own definition of this, which differs from the general definition!

You could get more information about this in Arabic [here][2] and [here][3]

**Mukhtalaf fih مختلف فيه and al hadith al mutawatir  الحديث المتواتر**

In istilah al muhaditheen there's no Mukhtalaf fih مختلف فيه AFAIK!

The conditions for sahih hadith have been derived from the conditions of al-Bukhari and Muslim etc. later and there's no specified number in the [definition of tawator][4] but some scholars said the minimum number is 10!

And Allah knows best!


  [1]: https://ar.wikipedia.org/wiki/%D9%85%D8%AA%D9%81%D9%82_%D8%B9%D9%84%D9%8A%D9%87
  [2]: http://islamqa.info/ar/218507
  [3]: http://ar.islamway.net/fatwa/31068/%D9%85%D8%A7%D8%A7%D9%84%D9%81%D8%B1%D9%82-%D8%A8%D9%8A%D9%86-%D8%B1%D9%88%D8%A7%D9%87-%D8%A7%D9%84%D8%B4%D9%8A%D8%AE%D8%A7%D9%86-%D9%88-%D9%85%D8%AA%D9%81%D9%82-%D8%B9%D9%84%D9%8A%D9%87
  [4]: http://islamqa.info/en/34651