your own picture shows 16°C and the days in question had 13-15°C in the morning and evening.
If you sit idle without clothes for hours even in 17°C you will get cold as fuck. If it would have been 5°C this could have caused serious medical issues. If it would have been freezing, some of them could have reached life threatening hypothermia.
Video of Palestinians stripped, forced to sit outside by IDF soldiers raises ire (abcnews.go.com)