Who else was on the opponent team when you saw this?

There are some characters who gain health whenever their team gains chakra.

Or are you referring specifically to Sage Naruto and Sage Jiraiya receiving health when they get chakra? That's odd - I've never seen that happen before in my experiences with either Sage.

Hm...

For the Ninja Exam thing, it's possible that Sage Jiraiya might have a slightly different skillset because it's PVE. Sometimes they change a ninja's skillset in PVE - like in certain instances, 3* Naruto has Unyielding. This might be the case with Sage Jiraiya, but I'm not 100% sure.