[DIVx0]

My hunch is that you're experiencing title inflation.

If I am correct, the hiring manager knows you have 4 years experience and isn't necessarily focused on hiring "Senior" but more interested in people who have a proven track record, which 4 years in is.

The way to really distinguish my guess from reality is to ask a lot of questions about the expected duties. If they fall within or near your current experience then you're all set.

If they are asking you to make big decisions about technical direction or influencing development teams then the hiring manager is really looking for a more experience person. Still, in my opinion, if they're giving you an interview and if you think you can meet the expectations then no harm, otherwise you should pass.