You're mixing up the weight of the threat (that you could get sued for this) with the weight of the C&D itself, which at best means "I cared enough to pay a lawyer some comparatively small fee to write this for me" and in this case means bunk. You could even pretend you owned the image and that I broke a million laws, if you wanted - it's not legally binding.
Besides, sending a DMCA takedown doesn't bar the sender from suing you if you aren't an online service provider (e.g. you're a blogger using Wordpress.com, rather than Wordpress.com itself) or if you knew you hosted the supposedly infringing material in the first place. Both of these apply in this case.
Besides, sending a DMCA takedown doesn't bar the sender from suing you if you aren't an online service provider (e.g. you're a blogger using Wordpress.com, rather than Wordpress.com itself) or if you knew you hosted the supposedly infringing material in the first place. Both of these apply in this case.