Not a phrase I’d heard before - neat! 
In most municipalities, garbage is “owned” by that municipality, so they can, in fact, prosecute for Dumpster diving. Enforecement is, of course, a separate matter, but they can if they want to.
Thanks for your responses, everyone. I’ll admit now, I had an ulterior motive when I started this thread. I started a different thread- with different circumstances and different legal implications, I know, I know - and the responses in that thread got me thinking. Now that I think about it, I suspect this is why I daydreamed the seed pod scenario in this OP in the first place - my subconscious was still wresting with everyone’s different perspectives on theft, and my brain eventually cooked up a scenario where something is taken from another but most would agree * looking at the poll results * that the outcome is not actually “theft.”