The artist of this French comic gives a good interview here, talking about the Twilight Zone / "cruel fairy tale" nature of the story and how the comic form allows you to represent sped-up time better than films (which require naturalism-undermining CGI) or prose (where the pacing is slower). Should be said that the artistic challenge of drawing rapidly-ageing bodies is met pretty well, although I didn't always like the cartoony artwork, which over-emphasised facial features in order to make the characters clearly distinguishable.
The interview didn't touch on the rather interesting cold open the story has: an aerial shot of the costal landscape, plunging deep into the sea water, through an underwater cave and up to reveal a placid shore. In a way quite cinematic, in that it's very much about the movement of "the camera". But if it's true that CGI is an imposition on live-action, then the effect would be (slightly) different if it was on film. I suspect CGI may be good (and ubiquitous) enough for audiences to not experience it as an imposition if it appeared in an otherwise quite naturalistic setting. But if I'm wrong, comics still do have a niche to fill in this area.
More interesting than that is the symbolism which accompanies the introduction to the geography of the story, particularly the underwater cave section where the reader undergoes a kind of birth: through the watery hole and up for air, the path of life stretching away on the shore. This is followed by a sequence in which a mysterious man on the cliffs notices a woman on the beach taking off her clothes and jumping into the sea: a kind of sexual awakening metaphor. He walks away, but the final sequence is of him turning back to see her floating on the seawater, and then looking down in resignation. Later we learn that the woman is dead. So we go through a kind of birth-life-death cycle right at the beginning of the story. The silence of the images also establishes the right eerie tone, setting up a nice contrast with the buzzing activity of the arriving holiday-makers who are thrown into this creepy setting and situation.
The mystery is never explained, although a science fiction author advances a couple of theories. It's a fable – something underlined by the bedtime story told at the end about a king who builds a fortress against death which only serves to cut him off from his family. A link is drawn with the obsessive sandcastle-building the doctor succumbs to. He forgets wife and children in the pursuit of transient and ephemeral life projects. However, some projects are more ephemeral than others. The bedtime story includes the king looking over to a distant mountain and realising that he has never touched a snowflake. Similarly, one of the children regrets that he did not try to escape by climbing the cliffs when he was younger and healthier. I think the creators are trying to valorise projects which seek an understanding of and settlement with the natural world. But this is motivated by the same impulses as the need to build castles of sand (those unphilosophical castles in the air castigated by the Scottish Enlightenment), a body of knowledge not secured to and tested by the experience of nature. The final scene is of the surviving member of the group tapping out the beginnings of another sandcastle – obviously not learning the mistakes of his forebears.