TLDR: Am I the asshole for keeping track of the original topic of a conversation, and bringing it back even when the conversation might have drifted to other topics?

This happened around Christmas and I've been thinking about it ever since. 

In my mind, even if the topic of a conversation drifts, most of the times I keep track of the original topic and if there was something I still want to say it about it, I try to bring the original topic back so I can finish that conversation. 

Now, my mom is kind of the opposite. She has a couple topics, mostly related to her work or projects, and most conversations with her end up drifting towards that, then away from it and back to it, several times. 

We had a disagreement on Christmas because of it. We were talking about a sweater that she's knittinng for me (got ruined in a dryier machine and she undid it and is doing it again), and I was telling her a story about the sweater and how it had got ruined, and somehow she made the topic drift to my biology teacher in middle school, then to a biology teacher she's working with, and from that to the project she's doing with the teacher. 

Then when I told her that whenever I talk with her I feel that the conversation always turns into the things she's doing and interest her, regardless of what I have been saying, she argued that that is the way conversation works, going from a topic to another, and that I hold on too much to the original topic of a conversation and try to bring it back even when it stopped being relevant to the conversation. 

Then she let me finish telling her the story about the sweater, but it felt like she was only doing it because I was forcing her to and she really didn't want to hear about it. 

So... what do you think, reddit? Have you met people who do this kind of thing? Are they (like I would be) assholes?

TLDR: Am I the asshole for keeping track of the original topic of a conversation, and bringing it back even when the conversation might have drifted to other topics?