Why would a store clerk go beyond policy and chat with me like this?

I had a female store clerk who told me she'll take the heat from her boss from me because their store policy i had to pay over $5 on debit card purchases at her store then she left her station and walked towards exit door where I was then we started talking about batman flawed neck movement technology and multiple flawless short conversations without any social anxieties. She also signal me that our conversation was ending and she didn't show any annoyances from our conversations. When she talked about batman I was impressed about our shared interests on batman and DC.

Normally employees at some places will decline any transactions under $5 for examples.
Why would a store clerk go beyond policy and chat with me like this?
Why would a store clerk go beyond policy and chat with me like this?
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