If a person A says “only X”, it means that there was only X in the range of observation of person A. It is not clear whether there is really only X or whether the range of observation of person A is narrow.
This page is auto-translated from /nishio/「〜だけ」と観測範囲の狭さ using DeepL. If you looks something interesting but the auto-translated English is not good enough to understand it, feel free to let me know at @nishio_en. I’m very happy to spread my thought to non-Japanese readers.