"Charilie Horse" is not a medical term, as you are no doubt aware, and in common parlance seems to mean "pain in this muscle belly." So the differential is pretty broad--tears, sprains, strains, spasm, etc, etc.
If, as seems to be the case reading your note, it went away and did not recur, move on. Life and training being what they are, another issue will arise to take its place presently. The training lifestyle is full of transient aches and pains. You begin to get a feel for which ones are unimportant and which warrant a freak-out. At first blush, this sounds like the former.
Not your doctor, infotainment and ejumacational porpoises only, the usual disclaimers, yadda yadda.