Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

You never had anything but an opaque blob of encrypted data and a forwarding address which may or may not be its final destination. Without the decryption key this is indistinguishable from random noise—meaning you never possessed any CSAM yourself. Even considering the pitifully low standards to which prosecutors are held in this area there is zero evidence of any intent on your part to receive, store, or transmit CSAM and no reason at all for anyone to take an interest in you or your node. Coming after you won't lead to any convictions and would just be a waste of everyone's time.

If you're going to assume bad faith and/or reckless disregard for facts or reason—never mind justice—on the part of law enforcement they could just plant whatever evidence they need to secure a conviction. No one is safe in that scenario, whether they're participating in the I2P or Tor networks or not. Having lots of lawyers wouldn't help the ISPs either in a hypothetical alternate reality where merely routing someone else's encrypted data made one liable for the content.

Forget hypotheticals for a moment. How many years have Tor and I2P been in operation by this point? Over 20? And just how many people have actually been convicted of possessing CSAM just for running an internal routing node on either network? Zero?

You do manage to highlight the absurdity of criminalizing mere unknowing possession of CSAM (even unencrypted) in a world where computers are constantly sending messages to each other which their users have no awareness of. Even more so if you try to apply that to encrypted content the user has no access to. You can't control what you receive and you won't necessarily be aware that you received it. Under the same reasoning you just applied to I2P you could go to jail on CSAM charges for picking up a USB flash drive or other storage media (even paper) off the street and returning/delivering it to the address marked on the side—either without looking at the contents (which is safer in terms of avoiding malware), or having found it to be full of what appears to be random noise. Or even seemingly innocuous data, given the possibility of steganography. It's absurd. Fortunately in the real world while they throw around the term "possession" you generally would have needed to have had reason to be aware that this particular data contains CSAM, and failed to report it, before they could secure a conviction. Actus reus non facit reum nisi mens sit rea still counts for something even when it comes to CSAM.