If you look at the image with the tooltip that says 45, you'll actually notice that its 2 subs very close to each other (there's a minuscule colour difference). One of them must contain 45, the other 49. When it reaches the outpost, it will be (45+49) - (20 + 6 produced drillers from the factory + 3 shield charge + 2 extra shield charge because of the time it took) = exactly 63. My theory would be that he had 50 subs and the game somehow let him launch two subs at the same time (it usually tells you that you already have a sub directed there if you're launching one). He launched 45 or so the first time, and he must've thought it didn't work, so he launched a different amount (49) the second time. the two subs then managed to launch at the same time.
Kings aren't OP
"Imagination is more important than knowledge"
----Albert Einstein