Honestly, that statement applies to pretty much any part of MATLAB unless the behaviour is nailed down by existing mathematical or engineering specifications - and I'm talking as someone that likes MATLAB overall. Mathworks tries a bit to polish and paint it as a coherent whole, but it's patchwork of things built upon and stuck to the sides of the existing structure, optimizing towards a particular kind of "pragmatism" than towards any kind of elegance.
There are few things as slow as non-vectorized MATLAB code. MATLAB's regex engine is pretty decent, actually, and supports quite a few fancy tricks. For example, I use the regex engine to find the start/end of all numbers and strings ahead of time, and for replacing escape sequences (even unicode escapes!) with their literal characters. The former is particularly important because otherwise, you'd have to manually iterate over characters until you find the end of strings or numbers, which is unacceptably slow in MATLAB.