I don't get why Son Yijo callled Jeong Sunwoo a 'sunbae', while he working in that company...

Sunbae, refers to someone younger. Age related rather than time in the company

I believe 'sunbae' means 'senior' in the context of seniority. For instance, in college, if there's an upperclassman who is actually younger than you, you should still call them 'sunbae.' That's as far as I know from reading some Korean manhwas. Sorry if I'm mistaken

ive been asking this since before, but the explanation i receive doesnt answer the question

I think its a translation issue, because some pronouns are wrong too

nope, Sunbae is senior
Hoobae is junior
and Hyung/oppa for older male
for younger one, they call the name not title

Don't you think it should be some job title? Like deputy manager or something like that?

could be?
i dont remember exactly but yijo is in a higher position right?

You're right! I got my terms mixed up. Somehow. I was totally thinking of Hoobae

You're right. I was wrong. I was thinking of Hoobae. Lol awk

Redhead is a lateral hire so he might have a higher position in marketing than Ijo who works as a dev hence being called sunbae