Translation:The boy said that he is not going to forgive the teacher.
I wasn't considering that - yes, Portuguese is much muddier (or freer, depending on the perspective) when it comes to this; using the presente gives it an immediacy that cannot be captured by the pretérito; this is not just something that someone said and that you're reporting to someone else; placing it in the present allows the people you're talking to about the ordeal to feel the impact of the words as they were spoken, something which the English would only allow as a piece of dialogue or free indirect speech; e.g. The boy said, "I'm not going to forgive you [the teacher]"
We've conferred about it as a team and we've decided to add "wasn't going to forgive" to the examples with "desculpar" in this lesson; I have other assignments, but I'll see what I can do to fix other, similar sentences - in the meantime, please keep using the "Report a Problem" function in your exercises to alert us to these issues.
Thank you again, and good luck with your studies :)