You're right. The bug described in the article is just of the "may fail under load / with multiple users / in real-life scenarios" variety.

In the zoology of bugs, that makes it a common Mandelbug (1), but not a rare Heisenbug (2). For an even more exotic species, see Schroedinbug (3).

(1) http://www.catb.org/jargon/html/M/mandelbug.html

(2) http://www.catb.org/jargon/html/H/heisenbug.html

(3) http://www.catb.org/jargon/html/S/schroedinbug.html