No one suggested the OP endanger either bike rider. I suggest that the case law you refer to is not applicable to a tandem bike riding down main street of a busy city; consideration of saftey to use your words.
We don't know traffic conditions because they weren't posted. But, assuming it was, in fact, a busy city street the cop did the OP a favor. Just sitting here and thinking of one mental image I can see several ways the cop could have handled the situation. What the cop did was the kindest and simplest and did not call into play any of the child protective laws or others that could have been used.