Looks to me like the tarp would have held up under the same situation when new but over time UV and wear have weakened it. UV is tough on tarps and tents. Cheap nylon can show weakness in a few weeks of summertime exposure. Polyester tends to age more slowly but in time it also fails.
Sometimes the damage is easy to spot as the surface fibers blanch and frizz because they have been weakened but other times the fabric looks good but is ready to fail.
that's exactly what happened. i'v been using this tarp for a good while now, and it''s spent a few weeks baking in total. for a five dollar tarp it served remarkably well.