Now this is completely speculation, however it seems like it could be a great possibility.
The location Master Chief is on is the Ark from Halo 3. People are saying this due to the planet in the background looking like the Strip-Mined planet by the Ark. Silentium confirmed that the Ark was not fully destroyed, only damaged.
Also confirmed in Silentium, after Offensive Bias defeated Mendicant Bias after the Halo's fired, the Iso-Didact (The good Didact) buried Mendicant in the sands of The Ark. Mendicant Bias was helping John through the Ark by the terminals, and actually manipulated the portal so that John's half of Forward Unto Dawn would make it to Requiem. It seems that, if that really is the Ark, then the thing that popped out of the sand was Mendicant Bias.
In the picture provided it looks like Master Chief has gone through some pretty harsh battles. Now it would seem like he would get new armor from the UNSC if it was that damaged. Frank O'Conner confirmed via NeoGaf that Chief was cloaked because he was trying to mask his identity from someone. Now who? Well it can't be Sentinels or Prometheans because they would recognize him right away just like 'Mendicant Bias' did. (Because they're AI's) So that leaves the Storm, or the UNSC. The Ark is a large research area for ONI and the UNSC, so it's unlikely the Storm would be there. Why would he hide from the UNSC? Well, his armor is damaged greatly, he's hiding, but he's looking for something...
The UNSC might not have believed him similar to how Andrew Del-Rio didn't believe him. They might think he's crazy. Possibly he's gone against the UNSC and ONI as they wanted to replace him at the beginning of Halo 4. Many people are speculating that John has gone Rogue and is on search for something, possibly the Iso-Didact and Chant-to-Green, the new Lifeshaper.
Again this is all speculation.