Upon early seed formation way back on the plant it came from an error which occured in either meiosis or metosis (cant spell or remember which one does it or both.... whatever ppfffffd) and subsequently this happened.
It happens at seed formation shortly aftervpoklination largely due to stress and that can be atested in the fact cotyledons are formed before germination so it must have hapoened at seed formation and early cell division.
One other fact ive seen is that some fucked up seeded plants can oroduce a greater ratio of these trifoliates, thus why i mention the stress factor which also ties into the main way to fuck up early meiosis mitosis (fucking words again ppfffd).
A distinction is made that trifolates are not and always will be zilcho to do with triploids or any ploidy (of which weed does not show). You can wiki ploidy or triploid for a clearer understanding on that.
For me this is the clearest and best explanation but so much opinion and guess work means im possibly one of the few giving this info or who has done enough investigation to even have an amatures guess at somthing pretty complex.
There was some complex reason why it reverts back to normal two leafed morphology, its not a change in dna but a change in its replication.... fucking idk its been to long since i googled genetic boring crap.
Obviously this would read better in non_dyslexic format if anyone wants to google the science and ckean it up for future generations of led growers