I took out SIM card for my iPhone, why isn't my data erased?

Okay, long story short, I got an iPhone 5s a few days after it released, so I had no need for my iPhone4s. My friend's old, cracked slide phone was in really bad condition, so I told her she could have my old iPhone 4s.

Now, I removed the SIM card really fast during class, that had all my old memory, since class was ending in a few minutes, and she just texted me saying my old phone's password is still on.

Why isn't my data erased? Shouldn't it be gone with the SIM card? I don't have anything to hide, but I really don't want her to see my old stuff, since I have personal information, so I'm kind of flipping out.

No.

The SIM card doesn't hold any information besides your carrier info and phone number.

All personal information, settings, etc, are saved to the interal storage of the iPhone.

If you want to get rid of all that, you have to factory reset the phone.

Your iphone is pregger, short story longer