Yes, it was a 788 and I see your point. But still, in all the halcyon years when widebodies were quite frequent on SFO domestic mid- and trans-con routes, I flew them often and never once departed/arrived Intl. I would just find it surprising that there are so many domestic widebody flights during this crushing period that they ran out of capable T3 gates.

Side note, it appeared that our domestic departure was the only flight leaving from Intl G around that time. No other passengers to be found in the concourse. Probably also a product of that time of day, but very bizarre to witness nonetheless.