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> We access your private content only when we [...] are required to by law.

The ellipsis is doing a lot of work there. The full sentence is:

> We access your private content only when we have your permission or are required to by law.

They will claim that you gave them permission by acknowledging the TOS.

The two subclauses of "when we" are joined by an "or", so only one of them has to be true to fulfill the "when" condition.

I think what he is saying is that if they get the user to agree through TOS then they always have permission via the first subclause you omitted.