Anderson says he took the XL5 from a Castrol oil of the time, so if Trek was referencing anything it could equally be that.Good point. I'd say there are three possibilities:
• It could be a deliberate nod to the Anderson show that had just been on NBC.
• It could be a total coincidence.
• It could fall between the two: "XL5" could come out of someone's head if he saw the show listed in TV Guide, forgot all about it, and then produced what he thought were random characters through a process called cryptomnesia.
https://en.wikipedia.org/wiki/Cryptomnesia