If a Koha is set with ReservesControlBranch syspref set to ItemHomeLibrary item-level-itype=yes, a patron placing a "first available" hold won't be counted in the total number of reserves placed.
The SQL is SELECT 
  count(*) as count
  FROM reserves
  LEFT JOIN items USING (itemnumber)
  LEFT JOIN biblioitems ON (reserves.biblionumber=biblioitems.biblionumber)
  LEFT JOIN borrowers USING (borrowernumber)
WHERE ...
  AND items.homebranch = ?

=> items is not defined, the hold is not counted