Like I said, it’s a nitpick. I can know what a person means most of the time, but it’s imprecise and technically the ellipsis can be almost anything depending on the explicit values/symbols. In the cases where the pattern is clear it’s clear. Where it’s not, using proper set builder notation in the first place would have made it clear. I’ve also seen it used in contexts other than sets, including for summations. In those cases often just having the summations in proper form can make consequences and manipulations plainer and easier.