Is flirting cheating?

My boyfriend's friend came over to my house, asking for advice. His girlfriend told him to text one of her friends back for her while she was getting ready. When he opened her messages the conversation that he was brought to was to a guy. She seemed flirty in the texts saying "I'm just enticing you ;)" to the guy. The next text was "oh what a shame. I didn't do a good enough job then huh? ;)"