The article is wrong about mixing strings and numbers though. The requirement for homogeneous data, and the use of boxes, is a feature of the SHARP APL lineage, which includes J (although these languages could allow mixed arrays if they wanted to). But the APL2 and NARS families simply allow anything as an element of an array. These are much more popular, to the point that every recent APL I'm aware of uses this style of array. Possibly a reason why J wasn't very successful; probably not a reason why APL usage disappeared.

See also https://aplwiki.com/wiki/Array_model.