Not weird at all, #8 rod bearing is fed from the #5 main; #7 is fed from the #4 main.
Possibly some crud/crap/debris left in the oiling path to #5, which, has been pointed out, is a partially separate oiling path vs. the path to 1-4. Would the 'scrapings' off of the #5 main bearing from a sharp edge on the oil hole wipe out the #8 rod bearing? IDK