Do I give people the wrong impression of me?

So I'm half way done with my Masters program in the clinic and there have been talks about them hiring me after I graduate in July.

A very senior colleague told me today that even when I get an offer here, try to open my opportunities at other places too. I seem too timid and weak for how cut-throat the workplace is and how brash these people are. They will overwork me and I won't have a life. I just smiled and said thank you for looking out for me.

In the clinic I am usually quiet. I don't join people's conversations because I don't see the point of that. I'm there to learn as much as possible about the job, why waste my time gossiping? I'm amicable and pleasant to everyone, always down to help out whenever possible, because again, I'm a student and I just wanna give a good impression of how proactive and cooperative I am. I guess I never voice out my opinions about things, or don't share much about myself with people, that's why I think I come across as this meek-looking, submissive, keeping it to herself kinda person. Probably because I'm still learning, I just don't have the confidence of someone who is employed and knows what they're doing. Or my inferiority complex of being a Master's student at 34, still single, never have a job, and an immigrant does play a part (this maybe a stretch lol)

That colleague doesn't know me outside of the clinic. They just assume my personality at clinical is my whole personality. But why am I still letting that affect me?