I have some theory regarding why author have the same artsyle of
Boyish girlfriend , it's simple, these two people is the same person, why, just remember that author is like 3 month ago is embarrassed of he/she getting caught by his/her family drawing the spicy cover of vol 4.1, so because of that he must be kinda "making a new penname" to draw this project since this one itself is full on s*X and eroge, so in order doesn't caught drawing this H, he/she just submitted new name (keep in mind this is just my speculation, just take this as a grain of salt)