what did she mean by this text? 10 points!?

[Love.Live.Laugh]

so i was texting this friend ( i will call her brooke) and she asked me what i did today. i said that ran with my brothers. she texted back and said : running? and i texted her back and said : yes, why? she replied: just wondering.

i am not the skinniest person in the world so i am wondering if she said "running?" out of disbelief.... what do u think?