Why not assume they are having a bad day, they are just out of a previous relationship and they want a break, your just not their type (even if you had all the abs and a chiseled jaw and confidence they wouldn’t be interested), what if they aren’t into your gender, or what if they are in a committed relationship with their horse?
There are a lot of things that can cause it to be a no deal that are not your fault. If you feel like you did a good job asking, then it is probably one of the above.