Hi Isabel,
I�ve used used Dreambox and Beast Academy for similar reasons with my children. I would just ignore the teacher�s comments. Beast Academy is a well regarded program. It will not harm your child�s development.
At teacher conferences this year one teacher mentioned how wonderful it was that my son could solve problems in so many different ways. I think his work with Beast Academy has helped develop this skill.
It sounds like you�re doing a great job meeting his needs. Keep up the great parenting and don�t let the teacher�s comments cause you self doubt.