Yeah better to be 5'10" 300 lbs. That's what the ladies love. You people are so dumb. She's a runner. In all likelihood she has speed goggles anyway. 6'4"? That's probably 98th percentile. So no, op is probably not 6'4". But yes, people are impressed by height for some reason.
OP, it might just mean she wants a running partner. She may be in a committed relationship for all you know, and running partners can be hard to find. Conduct yourself as if this is the case until you gain more info. It might mean she's interested in you. Or she isn't sure if she is as most girls are kind of timid and afraid of both rejection and weird dudes, of which there unfortunately are many. Not that there's not weird women too. Occasionally you get a bold woman who will ask you out. That's pretty cool IMHO. It's also no guarantee it'll go anywhere.