This may just be me, but in my head, the align operations are named ambiguously. The “align selected objects horizontally” lines up objects so that they are matched on the vertical axis, and the “align selected objects vertically” lines them up matched on the horizontal axis.
The icons make sense, but the wording is confusing. It could be interpreted as if the movement is done on the specified axis, rather than the alignment. I’d suggest something like Inkscape, which has “align on vertical axis”, which makes it clear that it’s the vertical axis that’s lined up.
I understand what you mean with your question. I use both Inkscape and Lightburn and have to make a mental adjustment when switching between the two.
If you consider that the align horizontally feature moves the items in the horizontal direction, until the vertical axes are coincidental, it makes sense.
I just noticed that if you activate the “Arrange (long)” toolbar, it has a clearer description for the same functions. If those descriptions were used consistently, everything would be great.