Welcome!
The difference in itself is not concerning. It is not unusual for very high cognition learners to have somewhat lower working memory, and in any case, the WMI is normatively quite high (technically in the Very High range), well above average, and bordering on the Extremely High (gifted) range. (Missing it by a mere two points.) Your evaluator's comment is entirely appropriate. I would not worry about it at all.
Your DC's scores are very strong all around. Have you considered applying to DYS? (It looks like the NVI is in the qualifying range.)
If you have other questions about the testing, you might consider posting them in a new thread specific to you.
