The specific term 'hodl" purportedly happened in December of 2013 on the Bitcoin Forum message board, where a user misspelled holding. Like a lot of things on the internet, people liked the mistake and started using it instead of the correct spelling.
It appears that the use of the term 'whale' actually comes from the gambling industry, to denote an individual who could afford to lose an inordinately large sum of money. In the investment world, which includes crypto, it means more or less the same thing, though on STEEM it's more commonly referring just to having a lot of STEEM or SP.
A lot of crypto slang comes from the investment world. Pump and dump, bagholders, to the moon or mooning are all intertwined with the investment world at large.
There isn't an official way any of this comes about. People just adopt it or not, and most of us do it because others have done it, just like you might see people who use STEEM referred to as Steemians, and you might find someone signing off their post with "Steem on!"