OK, now it makes sense. The other night I was checking out the Banner Class Bulk Cargo Ship BTG-237 in the Pleiades Sector IR-W D1-55 system. A thargoid appeared and started scanning canisters, so I approached out of curiosity. There were also rescue vessels about flying around with the alien vessel, and these weren't attacked, but a player in an Orca was. He made a getaway and then the ship went after me.
Now, at some point whilst the thargon swarm was chasing after me, something hit me and I saw that blue plus sign. I don't recall seeing the other player around, so someone, or something, helped me regenerate my ship whilst I was making a getaway. I wonder if the medical rescue ships at these places can heal commander ships? At work now so I can't test this out.