Why does row estimation on nested loop make no sense to me

On most nested loops that I do explain/explain analyze on, the row estimation for the nested-loop itself is a product
ofthe inner nodes of the nested loop. 
However in this case, I am stumped!

explain
select  era.child_entity  from entity_rel era  join user_entity ue on ue.entity_id = era.parent_entity and
ue.user_id=12345

Nested Loop  (cost=0.00..2903.37 rows=29107 width=4)
  ->  Index Only Scan using entity_pk on user_entity ue  (cost=0.00..62.68 rows=2 width=4)
        Index Cond: (user_id = 10954)
  ->  Index Scan using rel_parent on entity_rel era  (cost=0.00..1261.85 rows=317 width=8)
        Index Cond: (parent_entity = ue.entity_id)


How can the estimated number of rows for the nested loop node EXCEED the product of the 2 row estimates of the tables
beingjoined? 
Not only does it exceed it - but it is orders of magnitude greater. 

Am I missing something obvious here?  I an see the nested loop row estimate being LESS but certainly not more.



PostgreSQL 9.2.4 on x86_64-pc-solaris2.10, compiled by gcc (GCC) 3.4.3 (csl-sol210-3_4-branch+sol_rpath), 64-bit