I'm guessing the Klingon sarcophagus ship art somehow relates to our funny looking Klingons -- there's clearly some sort of burial ceremony they're at, along with a ornate coffin that has a more 'traditional' looking Klingon designed on it (
Kahless?). Perhaps they got stuck in some sort of temporal loop and a Federation ship just happens to be the one present when they come out of it. And those 'Klingon warp signatures' they detect are the actual Klingons of the era coming to check it out as well.
Considering they didn't even show the Discovery in this trailer, I feel like it's design and crew will relate heavily to the events of this first episode. Like it is some sort of joint Federation/Klingon initiative, as previously speculated.
Or the Klingons just look a lot different now and there will be no explanation. Wouldn't be the first time!