OMG Bf changed passcode back to the original one

Bf was talking/ flirting with this girl on social media. While he was doing it he changed his phone passcode. Yet, the girl said to him they’ll talk again next week so he’s not planning on talking to her for a few days. Now he changed his passcode back to normal (the original one that I knew). Why would he change it back again? Is it because he is feeling guilty for what he did, is it because he knows the girl won’t message him for a few days? What’s going on here. Advice please. He’s hiding this girl from me and changed passcode when talking to her. Now that he’s not talking to her he put it back to normal. What does this mean?