No, it stems from North American use of ÷ for division, which is then ASCIIfied to %.
+/1 2 3 4 5
plus over 1 2 3 4 5
the plus reduction of 1 2 3 4 5
1+2+3+4+5
15
over can also be used with *
*/1 2 3 4 5
the product reduction of 1 2 3 4 5
120
> An operation (such as summation) which is applied to all components of a vector to produce a result of a simpler structure is called a reduction.
"/" is known as "insert" in J [2] and "over" in k dialects (like Goal)[3].
[0] https://en.wikipedia.org/wiki/APL_(programming_language)#Mat...
[1] https://www.softwarepreservation.org/projects/apl/Books/APRO...
"/" as "over" in k reference (see Chapter 5)
http://www.nsl.com/k/k2/k295/kreflite.pdf
and "over" in the Q reference: