Maybe based on your experience they felt comfortable extending the offer as is.

I’d say it’s pretty sketchy for a job at the 9 level to straight up send an offer with zero contact, interview, or reference checks. If it was a super low level GS position I’d say it’s not a big deal. I don’t mean sketch as in it is fake, but sketch as in that office might be terrible to work for. My job starts at the 9 level and it’s very hard to fill (mandatory in person shift work, no telework, 24/7 schedule, etc.) and we still just don’t send out offers with zero interaction or evaluation.

But since you’re currently doing the same exact job at a higher grade, it may not be that big of a deal. I personally would not drop 2 grades to avoid going in once per week, but if you moved to another state then I definitely get that.