Ah... I don't think I ever studied the cave that carefully. But yeah, I'd agree with whoever up there said Spike's timeline didn't necessarily match up with what was happening in Sunnydale. Spike's journey would've taken weeks, if not months, to get to Africa, and the Sunnydale storyline in those last few episodes took place in a span of a day or so. It might have been foreshadowing for the viewers, but I don't think there was any premonition on the part of whoever drew it.