The "training exercise" part is irrelevant conjecture, Boruto said he was going to "come at her for real" and even asked if that was ok (which she said it was). That ends the doubt your trying to place on the seriousness of Borutos attack on Sarada my friend, he simply got bested.
The whole part of the training exercise was for them to test the ninja tools, not for them to actually kill Sarada or vice versa. Boruto saying that he was going to go at her for real, only means that he was taking this seriously. But we already know that Boruto was not using ninjutsu at all (and vice versa). Which means from that narrative, the fight was nothing more than a training exercise.
Even then, we have seen Boruto fight a willing combatant who was using a ninja tool (while using ninjutsu) and still the narrative says that it was nothing more than a training exercise. However, on that point, Shikadai made a mental note that Boruto was really trying to win that match.
Whereas when Boruto and Mitsuki lost, it was nothing more than a 'Damn ninja tools' or "Damn you got us good Sarada" response.