If you have dealt with mathematics for a long time, this should not be the first time you come across the same notation used for different things. The reason is usually that there are 'too few' symbols for 'too many' mathematical concepts. Worse still, consider:
$|x - 2|y|z + w|$
Does it mean "$|( x - 2 \cdot |y| \cdot z + w )|$" or "$|x-2| \cdot y \cdot |z+w|$"?
Would you then say that there must be a right way to handle this problem with absolute value notation? Or that we should not use this notation at all?
The goal of mathematical writing is usually to convey mathematical ideas to the reader, so if that is accomplished we often do not care too much for absolute syntactic consistency.
A frequent example is when an author says halfway through:
From now on we shall drop subscripts when they are clear from the context.