ok so serious answer....ready.....steady......go!
ejaculation, and even being hard, increases your bodies natural production of both testosterone THE essential masculine quality (in this case muscle buiding) hormone. and growth hormone, again an essential (and very expensive lol) hormone which is difficult to stimulate post puberty.
as well as these two huge benefits, being hard,masturbating, sex ect have also been linked to increased bio-availability of IGF-1 insulin like growth factor, this increased prouction in turn accelerates the rate (although only slightly) of absorbtion of protien (casein in particular).
if you couple this with the increased appetite effect that sexual activity can cause,
then no. it wont burn any muscle tissue, it will in fact help you grow (provided you are at a calorie surplus).
where you even heard that mis-information is mind boggling in itself
anyways good luck and have fun lifting (and wanking)