this was most likely referring to when kabuto and his mother were working under well respected war heroes he didnt quite get the praise due to war but the jonin are well aware that he working well under the lead medical corps since childhood so i would say not adopted really as he was sent to different places he was most likely the person who unintentionally was tricked into making the drug that made the original 8 tails jinchjuriki go crazy the 8 tails inside him got mad for no reason even though he was chill.
I REALLY hated Kabuto just like most... But after seeing this episode, one realizes that he, just like Nagato, was yet ANOTHER victim of Danzo's treacherous ways that turned them into the Hidden Leaf's worse enemies. If there's anyone to blame for creating pretty much ALL of the Leaf's Top Foes is that piece of [BEEP] Danzo. He TRULY DESERVED the worse death rather than his pathetic kamikaze to take Sasuke and Tobi with him.