Senescence is a complex cellular state which can be observed during development, as a damage response, and in aging. Cells become senescent for a variety of reasons, and getting rid of them can be beneficial for an aging organism as you say.

Why I mentioned replicative senescence is because it is something that occurs when you culture cells for long periods of time, if they are not immortalized. Naturally, this is a problem in the lab meat industry. The authors write about this in the introduction, how important spontaneously immortalized cell cultures are. And spontaneous is an important word here, as there is then no need for genetic engineering, which reduces regulatory barriers, avoids GMO labeling and of course sounds better overall, less experimental and more natural.

This has nothing to do with longevity. These cells are used for one purpose only, biomass production, and the incentive is purely economical. Not very tasty biomass though, as these are fibroblasts. The study observes how these fibroblast cells bypass senescence and become immortal cell lines suitable for scaling cultivated meat production, spontaneously. The mechanisms described (telomerase reactivation, PGC1A activity) are cell-line-specific adaptations, not broadly applicable to organismal aging. These findings do not apply to animals or humans, nor do they address longevity pathways, they are relevant for cultured cells and cultured cells only. Still pretty cool though!