From that RFC:
0.0.0.0/8 - Addresses in this block refer to source hosts on "this"
network. Address 0.0.0.0/32 may be used as a source address for this
host on this network; other addresses within 0.0.0.0/8 may be used to
refer to specified hosts on this network ([RFC1122], Section
3.2.1.3).
(note that it only says "source address")
which was based on RFC 1122, which states:
We now summarize the important special cases for Class A, B,
and C IP addresses, using the following notation for an IP
address:
{ <Network-number>, <Host-number> }
or
{ <Network-number>, <Subnet-number>, <Host-number> }
...
(a) { 0, 0 }
This host on this network. MUST NOT be sent, except as
a source address as part of an initialization procedure
by which the host learns its own IP address.
See also Section 3.3.6 for a non-standard use of {0,0}.
(section 3.3.6 just talks about it being a legacy IP for broadcasts - I don't think that even works any more)