Note that wifi cards can be extremely sensitive, with >100dB link budget -- that means that even if microwave oven door suppresses 99.99999999% of power (that's 10 nines!), the link can still be established.

(In one of the past jobs I designed wifi test rig that checks wifi card behavior during link loss. We had each end be in its own expensive highly RF shielded boxes, and we still had to set TX power to very low power to induce link loss)