It looks like the "tech" category reported on those graphs is including technicians, which make up very different percentages of the workforce at the two companies -- about 1% of Google's employees and 22% of Apple's, according to their EEO-1 forms:
Within the "professionals" category, which is the one with engineers in it, both have pretty similar percentages of black employees: about 1.7% at Google, compared to... about 1.7% at Apple.