You were playing with the Pokémon both of you brought while Arven made everyone sandwiches. Or...He made you two sandwiches. The Pokémon get their own delicious food specifically made to keep them healthy. Mabosstiff, despite getting better after the hunt for the herba mystica, still needs extra healthy food to fully heal.

"It's almost done, Little Buddy!"

Arven informed you with a bright smile. A contrast to his aloof, almost mean, persona when you first met.