[spec] Clarify binary element bitfield meaning (#1761)

Author: zstewar1

document/core/binary/modules.rst

@@ -360,7 +360,7 @@ It decodes into a vector of :ref:`element segments <syntax-elem>` that represent
 
 .. note::
    The initial integer can be interpreted as a bitfield.
-   Bit 0 indicates a passive or declarative segment,
+   Bit 0 distinguishes a passive or declarative segment from an active segment,
    bit 1 indicates the presence of an explicit table index for an active segment and otherwise distinguishes passive from declarative segments,
    bit 2 indicates the use of element type and element :ref:`expressions <binary-expr>` instead of element kind and element indices.