Again, the above could be seen as a negotiation technique.
Just how serious are you Benedict? I am sticking my neck out here, if you want this deal done then I need a sign that will be accepted as a genuine mark of good will from Rome. Salespeople do this all the time, as do lawyers and politicians and diplomats. It's a classic negotiating technique.
It could be that Bishop Fellay genuinely thought that B16 was different to Card. Ratzinger and hoped, against hope, that something had really changed. But I've spoken to him several times in the past and watched many of his videos and listened to his talks from years ago and this would be a complete change of mind. He's never trusted Rome and always viewed them with a healthy suspicion.
So it could also be that he very much doubted that Rome had changed but felt he did not want history to judge him and the SSPX for not trying. If B16's Olive branch had been sent back with a curt response, then the SSPX would have faced attack for being schismatic and proud.
I'm involved in M&A work where companies buy other companies and VC firms sell off companies as well as executive level hiring decisions, so I know from experience that all sorts of ideas are floating and trial balloons launched in order to find the right deal all parties will be happy with. This is the way humans are.
When my wife wants a new washing machine I go to the store with her and discuss the merits of the brand with the large door, top loader versus front loader, all in one washer dryer, extended warranties, low energy etc., so she feels she has given her input and looked at all her options. Then I go home and buy a Miele or Bosch, on-line, and have it delivered with no extra warranty. I could do this and save a trip to the store, but then she would not be as happy with the end result despite the fact that the end result is exactly the same.
A while ago these forums were alive with people who were SURE that Fellay was going to sell the SSPX out to Rome for a handful of beans. He didn't though, they were wrong. They misjudged him then and they might be misjudging him now.