That depends on how well tuned the node firmware is.
Ideally the receiver would run only long enough to detect a packet preamble, plus a timing error allowance on each side. If nothing is heard, then the radio would shut off and the node would go back to sleep until the 2nd receive window, and then again until it’s time to transmit (or do some purely local task) again.
Also in theory a node’s attention could be captured by something else (including radio noise) falsely triggering the preamble detector and thus tricking the radio into receiving for a full packet length, with the garbage only discarded when either the hardware checksum or the LoRaWAN cryptographic checksum is verified. This kind of false reception happens fairly frequently with gateways, presumably it happens with nodes as well though they just aren’t receiving that much to begin with so it’s not often seen.