[outworlder]

Wikipedia is not and cannot, as per their own policies, be the primary source. 'Wikipedia agrees' is shorthand for 'the sources mentioned by this particular Wikipedia article agree'

[loeg]

I think it's shorthand for "the collective Wikipedia editors agree," which is not exactly the same thing as saying every claim is backed by any particular source.

[93po]

I think more accurately, "the group of Wikipedia editors that managed to 'win' a debate agree".