I don't even think it has anything to do with the Sam scene. If she was meeting up with Sam, she'd be getting ready for it, not "relaxing"...
This is a good point, the description for the latest preview doesn't mention Sam at all, that hadn't occured to me until you said it. The only indication L&P gives that the sunbathing preview has anything to do with Sam is in the last paragraph of his prior Patreon post:
"
About the preview for the Sophia/Sam event, I'm still not sure which preview to choose. For the bonus storyline, you won't get a preview, that goes without saying. About the 2nd side job, I'm not sure, if I want to spoiler it as well."
Meaning the sunbathing preview has
something to do with the Sam scene, at very least we know it has nothing to do with the secret storyline, and doesn't seem likely to have anything to do with the 2nd Side Job.
You are right though, it could easily be another transition scene, or a Red-Herring-Preview, like the Sophia/Ellie scene from the night before.
My thing is though, she would be relaxing in the sun even with Sam coming over if she doesn't
know Sam is coming over. Sam only gets a chance to ask her about a music lesson for today if the player decided to send Dylan away and got the Sophia/Amber/Dylan/Sam pool party scene. Any other route (as far as I know) and she has no idea he's thinking about it.
The real takeaway here (hilariously) is that we're both letting our bias about the characters sway our thinking, you're not fond of Sam so you think the preview has nothing to do with him, I'm a BIG Sam fan and I hope it has everything to do with him.