Is farting what they really seek to control or is "farting" merely a code word for some other act they wish to control?

Well, Malawi is one of the most F'ed up places in the world, and being rife with AIDS and ignorance, it wouldn't suprise me if people thought disease can be spread by farting, so law or not, it might be risky to fart in public. Just guessing, but here's an example of how messed up they are:

As of 2010, homosexuality was illegal in Malawi, and in one recent case, a couple perceived as homosexual faced extensive jail time when convicted.[34] The convicted pair, sentenced to the maximum of 14 years of hard labor each, were pardoned two weeks later following the intervention of United Nations Secretary General Ban Ki-moon.

source wiikipedia