My answer to a very similar question just yesterday - same reasoning applies here - for clarity, possessives are used with body parts, clothing, accessories etc in appropriate situations. In this specific case there are multiple people involved, and both ‘groups’ of people are taking things off at the same time :

See the 2 lessons linked:

         “ Without using the pronominal/reflexive  “Je me regarde les pieds”, you don’t necessarily know whose feet ‘Je regarde les pieds” means - it is not totally unheard of to look at other’s feet, so unless the context makes it clear,  “les pieds” does not necessarily refer to your own feet, whereas “mes pieds” clarifies the situation. 

As well as the lesson you referred to:  Using le, la, les with body parts and clothing (definite articles)

 there are situations where possessives are used, covered in link : Special cases when you use mon/ma/mes/etc with parts of the body (French Possessive Adjectives) “