Don't think it's unusual. I witnessed one in the afternoon once as well. The 4 pm timeframe is consistent with other accounts over years, seems like routine patrol. Experienced the same thing in Phoenix recently while ascending a trail. Pretty consistent in remote areas that attract a lot of hikers. Just wave your arms if you need help!
http://matttravel.com/travellogs/2008_11_Deep_Creek.html (second paragraph after the 4th photo)
http://www.trailjournals.com/entry.cfm?id=103369 (second paragraph)
http://articles.latimes.com/2002/jul/20/local/me-outthere20 (third last paragraph)