The documentation for valueset.compose.filter says the following: "If multiple filters are specified, they SHALL all be true."   However there is actually more flexibility in the rules than this.   If multiple filters are specified in the same include element, then yes they are expected to behave with conjunction (AND) and must all be true.    At the same time, if multiple filters are present by virtue of being in separate include elements, then they are instead expected to behave with disjunction (OR) and so don't all have to be true.

There is a much clearer explanation for this here:  http://build.fhir.org/valueset.html#compositions

Please copy a phrase or two from this fuller explanation (or copy a link) into the valueset.compose.filter documentation so as to give a clue to the reader that there is a wider scope to these rules.