potty training signs?

Last Sat when I put Sierra to bed at 9pm she was not wanting to go to sleep so for the next 45mins I could hear her in there reading and talking. It got quite around 10pm so Brock went in there to get the book out of the crib. When he got in there, he saw all the books spread around the crib, her pillow in the middle with her head inside the edge of the case. Sierra then had her butt sticking up in the air with no pants and no diaper, yes no diaper. Brock had to get me right away to show me this funny sight. Sierra ended up waking up and Brock put on a new diaper and put her back to bed. The next day I heard Sierra wake up at 7:15am but could hear her playing in the crib so I just stay in bed for another 20 mins or so. When Brock went in there she was sitting up with no diaper on again. When Brock asked why she took off the diaper she said "I poopy", which she was not. Brock put her on the potty chair right away, but nothing happen. Tue morning Sierra woke up on her own around 7am when I got in there about 5 mins later she was sitting in the corner of her crib with the pillow over her lap, when I removed the pillow saw again she taken off her diaper, she said again "I poopy". We have not had problems with it since then. After taking to my friends I guess this is one of the signs of her getting ready for potty training. I guess she does not like how it feels to have a full wet diaper.