What is the ruling on neglecting one's studies and focusing instead on seeking Islamic knowledge and memorizing the Qur’an, and is the questioner sinful if his mother becomes angry due to this action or due to actions of his by which he does not intend to anger her?

Obeying one's mother and focusing on studies are religiously required. Displeasing one's mother due to negligence in studies is a sin. It is advised to be keen on obeying your mother in what is good, and to avoid, as much as possible, anything that displeases her, while maintaining your obligatory duties and learning the Quran and Sunnah (definition).