Why do women leave with friends mid-conversation?

I have a question about something that happened yesterday at the Sugar Land mall. I was in the food court, I had just gotten out of using the restroom, when I saw a woman walk in a store, so I followed (just browsing, not creepily). While looking at items, she walked near me checking out clothes.

Here's how the interaction went:

• I said, "Hello," and she replied hello back
• I asked if she had a lot of shopping to do - she said yes
• I mentioned the store smelled funny (it really did!) - she said "No, it's just the [blah blah whatever]"
• I introduced myself ("I'm [name]") and she immediately gave me her name
• Then her friend suddenly appeared and took her away to the restroom

(I mentioned I live in Houston, her friend appeared around this point, but that I was at the mall because I'd gotten a haircut nearby - but she was already walking away at this point, maybe a minor hesitation on her part, but she walked away anyway!)

She seemed genuinely interested or at least curious, so my question is: Why do women do this - leave mid-conversation when a friend shows up? Is this a common thing? Would love to understand the perspective.

My dirty mind thinks her friend might have been jealous, but I don't want to elaborate.

(I should have hit the gas pedal a little harder in my interaction, with her, before her friend showed up. I'm new and barely learning how to talk to woman in public)