If you perform factory reset, then everything gets reset to factory defaults, including usrnames and passwords.
How that what you said corresponds to FAQ which states:
How can I recover a lost password?
If you have forgotten the password, there is no recovery for it. You have to reinstall the router.
I'm not sure about how verbosely you want to understand reinstall
in the quoted FAQ. Namely: if you do the factory reset, you'll have to reconfigure the whole setup (again) and this part of the exercise is exactly the same as with netinstalling the unit.
BTW, Mikrotik is a Latvian company and I doubt they have many English native speakers on their payrolls (if any). I may be wrong though.
Anyhow, there have been numerous cases where wording in their documentation was ... well ... not precise enough and that caused some fierce discussions about what exactly their document was telling ...
BTW2, I'm not holding you from netinstalling the device. If you want to, go ahead, I'm not going to try to stop you. Actually that might be a good idea, there are some device states (mainly after they've been hacked) from which it's only possible to recover by netinstalling the device.