USUALLY (but not always) poison oak takes 3-5 days for the rash to appear - though my nephew, who is extremely allergic to it, does react within 24 hours. So it's possible that you were just reacting to other plant matter sprayed onto you by the weed eater. I often get a short-lived rash when I've been out in my backyard attacking the brush (and those are fairly civilized plants). Also got a poison-oak like rash (though it didn't open and weep) on my fingers last week after pulling weeds barehanded (and there's no way there's any poison oak in my suburban backyard).

I also am quite allergic to poison oak (end up looking like the inside of a roughly sliced ruby grapefruit) so I take precautions - day hikes ONLY when in poison oak territory, no backpacking, wear full cover clothing, and wash well with tecnu when I get home. I just don't take chances anymore with that nasty stuff. But I was thinking as I read this thread that I'm lucky to have high altitude (= poison oak free) territory nearby to backpack in, folks in other parts of the country just aren't that fortunate.