I can't help with an explanation of this particular 'punishment' other than provide two pieces of background information.
King's Regulations (in this case this
version published in 1912) are very specific about which minor punishments may be awarded (see paras 493 -507) and bounty boards are not mentioned. As stated in para 500 an officer is not permitted to introduce any other punishment not contained in the Regulations.
The only use of the term bounty at that time was the financial award made to soldiers who extended their service beyond their committed date. If the soldier subsequently changed his mind about extending his service he would be required to repay the bounty, or a proportion of it based on the additional time he had in fact served. If a bounty needed to be repaid then the calculation was done by the regimental pay office (for example, see KRs para 395). I can find no references to bounty boards in general.