They certainly look like the halyard knot to me. I wish I had known that you were planning to use them for sheets though. I would have mentioned that the halyard knot is difficult or impossible to untie after it's been loaded. You will usually have to cut them off.
When I replace my genoa sheets, I always buy a single piece and use a Larks head knot in the middle. After a few years, when I want to move the spots that show a little chafe, I will cut the line, end for end the two pieces and then use bowlines.
Sheets are usually overly large so that you can grip them, so they are strong that the amount of strength that you lose using a bowline is not important.