To be fair, "senior" doesn't seem to be particularly high up the ladder of job titles at tech companies these days. You get titles like "lead", "principle", and "staff", which are all considered more senior than senior.
At the end of the day, job titles are mostly for getting past recruiters. Interviewers (if they're any good) will judge you on your actual experience and capabilities.
This is a sector where people with no relevant formal education and three years on-the-job experience sometimes get called senior.