This means they represent an idea (or concept?) instead of a sound. The meaning is completely divorced from the pronunciation. In Japanese each character usually has at least two 'readings' for pronunciation onyomi (chinese-origin reading) and kunyomi (Japanese reading).
But often have even more than that, and specifically with peoples names the readings some times feel completely arbitrary.
https://en.wikipedia.org/wiki/Kanji#Readings
Basically, there are multiple ways to get the same 'sound' from different kanji, or get a different 'sound' the same kanji.
See https://en.wikipedia.org/wiki/Chinese_character_classificati...
BTW I recall later Egyption hieroglyphs were not strictly ideographic either, leading up to the Phonetician alphabet. I wonder how similar that process was.
I imagine most non-linguist nerds (myself included) would confuse the distinction between logographic writing systems and ideographs.
This is equally true for hiragana and katakana (the other two Japanese writing systems, which are phonetic) and all the names would be written as さとし in hiragana.