How does swapExactTokensForETHSupportingFeeOnTransferTokens triggered?

more specifically, how does swapExactTokensForETHSupportingFeeOnTransferTokens triggered/called from this contract : https://bscscan.com/address/0xE9b822C175FeB50D748Fae5D19cB56f6c0907F1C#code

upon investigation on the contract and the audit report of the project i found the tx that triggers the specific function of swapExactTokensForETHSupportingFeeOnTransferTokens

I can see that it triggers on transfer function but how exactly?

Note : the contract model is a dividend paying token in which the rewards are in BUSD.