Of course this is all just humorous speculation and not to be taken too seriously, but...     

It's not just that she's into sports and wears pants.  Fern wears pants and Sue Ellen is into sports, but they don't fit the same pattern.  Just one or a few of these things alone wouldn't really lead people to suspect her of eventually becoming LGBT, it's that so many of them happen all at once. 

While there's an alternative explanation for any one piece of evidence alone, taken as a whole, it increases the chance that the most simple and likely explanation is an innate male personality -- which often means eventual attraction to women.  It decreases the number of assumptions that must be made to explain her attributes.  It's the principle of Occam's Razor: among several competing hypotheses, the hypothesis with the fewest number of assumptions is the most likely one.  The hypothesis that all of her male attributes are the result of a male personality makes only one assumption: that she has a male personality.  The hypothesis that all of her male attributes are the result of multiple causes (i.e. that she's a tomboy, that D.W. saw her being bossy, that she just likes being useful with her body, etc.) relies on more assumptions, and is therefore less plausible.   

It's also worth noting that LGBT adults often enjoyed dressing as the opposite gender as children, even though it may have just seemed like child's play at the time.

While having a traditionally male personality doesn't absolutely prove that she's a thinly-veiled LGBT character, it increases the likelihood that she is because these traits are often (but not always) present in LGBT women.  Hence, the speculation.