Asking for a friend..

My friend told me her baby father (37) asked to use her (39) phone and she obliged and handed it over with no questions and no concerns. She then said she asked to use his phone since he was using hers just to see if the response would be the same without any pushback and he got aggressive and made it into a big thing that "she was doing this" and "only teenagers ask to see each other's phone". He supposedly works and when he went to hand her the phone he erased a cash app request asking his "coworker" for 20.00$?! She does not understand why he is being suspicious about the whole thing when she lets him use her phone with no issues. She wants to know what this could possible mean?!?