You are correct, wall squats are not in line with Positive Parenting.  They are a disciplinary tactic used to control behavior be placing the child in a physically uncomfortable position, in an effort to teach a lesson, but what  will a child gain by squatting along a wall?
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   Will he learn why he actions were wrong?
   Will he learn what to do in the future?
   How will wall squats improve the child and lead to positive self discipline?

It is impossible to provide an alternative disciplinary measure as the picture does not provide context or background information, but the method of discipline used should incorporate respect, empathy and healthy attachment to ensure that the behavior is addressed in a developmentally appropriate manner and is perceived as fair by both the parent and the child.  

What would a Positive Parent do in this situation?
Option A:  If someone else is in the home, ask for assistance calming the child.
Option B:  End the shower and attend to the child’s needs.
Option C: Exit the shower, remove the child’s clothing, return to the shower with the child.

Toddlers do not have anger problems, toddlers have limited communication skills which prevent them from expressing their needs and frustrations in a calm, logical, manner.  Until a child has fully developed the ability to communicate, tantrums are to be expected and considered normal behavior.  While this behavior is normal, it is still necessary to equip the child with the tools necessary for healthy expression.
A Positive Parent would hold (healthy attachment) their toddler and validate their feelings (empathy), while introducing the child to the words that match the exhibited behavior.  A Positive Parent would then give their child alternatives to try if the child is ever in this situation again.  A Positive Parent knows, that their child might take weeks or months before they are able to put the lessons into action.  Children learn through repetition, telling them something once, twice or thrice is not enough. 
It is okay to sound like a record on repeat.  As adults we learn new songs by listening to them repeatedly.  Our children learn by listening to us repeat the same things over and over again.

What would a Positive Parent not do in this situation?
Shame their child by posting the video on social media (respect).