Nope there is no contradiction. Again you haven't really thought about how this works. You are guaranteed to know who sent you your HTLC because the payment is settled through the channel. You cannot cloak this in any way.

You only need to ddos the lightning network so it won't record their HTLC when it expires. There is no need to ddos them, though I would argue it would be equally easy to do. And so while the other party will eventually see the secret on the block chain, they can't get their HTLC unlocked on the network before it expires.

And the lightning network has already been easily ddosed! We will see it happen more often if the lightning network ever gets bigger. This isn't some hypothetical situation.