It may be his reading genre preferences. The vocab I can see picking up some from fantasy and fiction, but Information is (obviously) gleaned from informational text, which doesn't appear to be part of his pleasure reading repertoire.
Also, it does take some time to fill in gaps. Just because reading has clicked in for him doesn't mean the previous disparity between verbal cognition and verbal knowledge acquired from text at his cognitive level will go away instantaneously.
Good to hear he enjoys reading! So often, even effective remediation comes too late to salvage the joy of reading.
