Yes your explanation about buying at a DIP is okay but buying at a DIP is mostly for those who uses the DCA strategy and they have reserved funds that they can use to buy Bitcoin at cheaper price when a DIP occurs.
There was never a time when buying the dip was meant to be for those who DCA. Buying the dip is a pattern of buying and an investor who wish to lump sum or dca can as well buy the dip. Some investors rely on only buying the dip as their strategy without considering dca or any other strategy. Like i said before it all falls down to the individual risks. Buying the dip can seem to be a lot less risky since one has to wait for the bottom to buy, but what those who wait for the dip dont know is that it can be more risky when the dip never comes and they cant buy at all. Waiting for the dip will leave them no other option than to not buy at all. Now imagine that an investor has to sell off his btc for profit and wait to buy a dip that never comes while the market keeps going up is that not a huge loss for him?
Those who buy when the price is down of course they will buy it in large quantities but for some investors who do not have large funds of course they will use the DCA method in the process of accumulating their Bitcoin gradually and I think everyone knows very well that no one can know clearly when the drop will occur and as you said they could miss the opportunity to buy it because the price did not drop when they waited for the price to drop of course this would be very disappointing.