Why, you ask? Because these appear to be the cryo-freeze units from the prequel, and while the one in the background is open, it appears as though Clark is looking into the pod in the foreground, possibly at someone inside.
Kara Zor-El–here depicted as an ancestor to Kal-El, not his cousin–appeared in that comic as its central protagonist, and at the end of it, her fate was unclear. Of the two people who were still alive at the time of their ship’s crash (Kara and Dev-Em, a murderer hoping to take revenge on her after she had subdued and captured him), only one of them is seen to emerge from the craft. That it was thousands of years ago when the ship crashed means that even the one who left the ship might not still be alive, but it seemed at the time vaguely plausible that someone might have managed it if they got to the pods that were meant for sustaining the Kryptonian astronauts’ lives during long deep-space journeys.
The prospect of the miraculous survival of Superman’s “cousin” looks pretty bleak, though; a high-resolution version of the image has been released now (click on it to enlarge), and whoever is in that chamber certainly doesn’t look alive and well.
Granted, they also don’t look like the mummified Kryptonian corpse that appears to be clinging to an energy weapon in the most recent trailer–but with what looks like damp, leathery skin and a single tuft of hair coming out, it would be surprising to learn this character survived the thousands of years trapped in the cryo-chamber as ice built up around the crashed ship. The forlorn look on Clark’s face is likely more about the loss of a key to his identity and a link to his homeworld than anything else.