Electrophilic addition on cyclopropane using sunlight
It should say &quot;in addition to&quot; rather than &quot;instead of&quot;.
Cyclopropane suffers badly from ring strain. The bond angles in the ring are 60° rather than the normal ~109.5° when carbon makes four single bonds. In the absence of light, when in contact with $Cl_2$ or $Br_2$ the ring will break and addition occur.
In sunlight, both the expected substitution reactions and the addition reaction will occur.
Can't find the reference I thought I remembered, but here's a site or two discussing it:
https://www.chemguide.co.uk/organicprops/alkanes/halogenation.html
https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/27%3A_Reactions_of_Organic_Compounds/27.07%3A_Reactions_of_Alkanes