Yup, as @Marie1 has rightly pointed out the mana gain is exclusively from tiles. The only hero who have mana regeneration on per turn basis is Alberich. And then there some other heroes who gain mana even without mana regen like Onatel, Misandra (to allies) and Inari minions. 
You can check out this thread for details on how mana generation works (especially, the Special Cases section)