Understand signs of numbers in ordered pairs as indicating
locations in quadrants of the coordinate plane; recognize that
when two ordered pairs differ only by signs, the locations of the
points are related by reflections across one or both axes.
The next time we see reflections in 8th grade geometry, where, it is introduced. Is it expected that students talk about, say, (1, 0) and (-1, 0) in terms of a reflection across the y-axis or is the reference to reflections addresses the underlying mathematical structure but not how students will be talking about this situation (similar to them using commutativity in 1st grade but not using the term)? I guess, given that students should be familiar with the idea of symmetry from at least grade 4, there is a familiar language that students can use.
Your second interpretation is correct. You might want students to observe that the two points are the same distance from the axis but on opposite sides, or that you could get one from the other by flipping across the axis, or something like that. You might even use the word “reflection” when likening the relationship between the points to reflection in a mirror. But students are not expected to understand reflections as transformations, or use the word, in Grade 6.