Kaggle Titanic submission score is higher than local accuracy score
First question: on certain competitions on kaggle you can select your submission when you go to the submissions window. There you may not be able to on titanic one so you are stuck with 100 percent.     

Regarding your second question and why do you have different results locally, there is a couple of explanations, first its randomization did you set all the seeds, second all of the modules/library versions you have locally sam as the ones on kaggle? Third different hardware could also be the reason