To be fair, you could easily say that Boba piggybacked on the escape on an ancient Sith and come up with numerous reasons why he wouldn’t tell the true story. From embellishment to some deal with the Sith lord, or maybe just fear

You could also explain the timing of the Sith’s escape by saying that after Palestine’s death there was suddenly some surge of “free Sith energy” or something because there was no Sith master left. You could even go as far and say the rule of two was specifically created to seal the power and prevent that Sith from escaping. You could’ve easily make that Snoke’s bakckstory, that he was malformed in the aeons trapped inside the sarlacc.

There were so many options and basically anything would’ve been better than “somehow he returned”