Interesting. Might be underground fiber. Permits are usually the same for blocking the street for manhole access and blocking the street for a bucket truck (Temporary Occupancy) but maybe neither of this was necessary and/or the fiber was pulled when the building was built.

I'm curious to see if the block your building is on has Sonic self-reporting has having gigabit service available. The FCC has a map at https://www.fcc.gov/maps/fixed-broadband-deployment-data/ but the data is 9 months old (ISPs are given 6 months to report data twice a year and the FCC publishes it about 3 months later)