So I looked up the norm tables, and, as I thought, the explanation of coding and symbol search given is, at best, incomplete. Given the scaled scores you reported, it is impossible that the number of correct items could have been 5 and 8, respectively. (Scaled scores would have been much lower.) So something became garbled in that communication. The grain of truth is that processing speed is weighted less heavily in the FSIQ on the WISC-V than on the WISC-IV (1 out 7, vs 2 out of 10, previously), so that a low score on coding (the subtest that contributes to the FSIQ) should have less impact on overall performance. That being said, I would seek clarification from the psychologist. Or another psychologist.
Coding and Symbol Search both involve significant visual tracking. Especially Coding, which usually requires constant visual referencing, up and down on the page, in addition to horizontal scanning across the lines. And there are no visual frames at the age 6-7 level.
