I'm a student studying English abroad. I couldn't understand something while reading an English article. I don't know why "about" was used in the emboldened sentence. Isn't "that's been the strangest thing" fine? I've thought "about" meant "concerning" or "nearly", but I think neither is right in this case. Therefore, please explain to me the meaning of that.
Utah officials found a mysterious metal pillar in remote Red Rock
Country in the southeastern part of the state while flying by
helicopter on a routine search for sheep. Officials said they had no
idea how the 10- to 12-foot-tall block of metal got there. "That's
been about the strangest thing that I've come across out there in all
my years of flying," helicopter pilot Bret Hutchings told KSL TV.
Besides, in the same sentence, isn't it better to use "is" rather than "has been"? I think using "is" looks more natural.