Is MongoDB IXSCAN operator a scan or a seek?
I guess MongoDB can do index seek and index scan ? 

Yes MongoDB can do index seek and index scan, but it can do both during one fetch.  That is what happened in your case. If started with a seek to the leftmost record of your index cuisine_1 and did a scan on 25359 keys.  During the scan of 25359 keys 1553 key matched your search criteria. Index not being a covering one, it had to do a lookup (for other columns) from 1553 documents. 

If so, how do we know that a seek id performed ?

It will always do a seek if it it using a index, I guess your question is when it is not doing a seek + scan but only seek? 

IXSCAN means:


  If the query planner selects an index, the explain result includes a
  IXSCAN stage. The stage includes information such as the index key
  pattern, direction of traversal, and index bounds.


If you see this, it will indicate a seek to one index key and no scan.  But anything more than one will indicate a seek + scan.

  "nReturned" : 1,
  "totalKeysExamined" : 1,