The author assumes that Trump assumes the UFOs under discussion are aliens, but the President didn’t say that.
If the government didn’t think they were aliens, they would be called “Unidentified Enemy Aircraft” or just “Unidentified Non-American Aircraft” or “Unmarked/Unnumbered Aircraft” or perhaps “Unidentified Aircraft”...and they would be reported on the evening news to no great interest of anyone but the military.;-)