man: Clarify in dpkg-query(1) when binary:Package gets arch-qualified

In commit d658a8ec1110c9b3b20987cd903a54f59801117f the semantics of
the arch-qualifications changed, update the documentation to reflect
that.

Closes: #801958

debian/changelog

@@ -49,6 +49,8 @@ dpkg (1.18.4) UNRELEASED; urgency=medium
     - Clarify role of Build-Depends in deb-src-control(5).
       Prompted by Johannes Schauer <j.schauer@email.de>.
     - Document supported feature areas.
+    - Clarify in dpkg-query(1) when binary:Package gets arch-qualified.
+      Closes: #801958
 
   [ Updated programs translations ]
   * Dutch (Frans Spiesschaert). Closes: #800513

man/dpkg-query.1

@@ -244,9 +244,9 @@ fields in control files):
 .B binary:Package
 It contains the binary package name with a possible architecture qualifier
 like \(lqlibc6:amd64\(rq (since dpkg 1.16.2).
-The architecture qualifier will only be present if the package has a
-\fBMulti\-Arch\fP field with a value of \fBsame\fP.
-This makes the package name unambiguous.
+An architecture qualifier will be present to make the package name unambiguous,
+for example if the package has a \fBMulti\-Arch\fP field with a value of
+\fBsame\fP or the package is of a foreign architecture.
 .TP
 .B binary:Summary
 It contains the package short description (since dpkg 1.16.2).