I'm going to bet on the .0001% chance that he has a daughter and she's actually alive and moved out, then she turns out to be the guild receptionist it's just embarrassing for both of them for other adventures to bring up.
Well, it's nice that someone saw the obviously struggling child with no friends or family and decided to try helping her. Now she just needs a training arc.
If that what manifested as fire magic, the water, air and earth would be goated. Like water jet (or at least high pressure water hose), pressurized air blast and sand blasting. But that's just me.
I am so glad she didn't wake to some super power and just defeat the thugs right then and there.
This story seems to be shaping up to be exactly what I wanted from an isekai- the protagonist growing into someone strong and powerful through trials and hardships instead of just being super-special-awesome from the get go!