If you add a | sed -n l to that tail command, to show non-printable characters, you'll probably see something like:
N\bNA\bAM\bME\bE That is, each character is written as X Backspace X. On modern terminals, the character ends up being written over itself with no difference. But in ancient tele-typewriters, that would cause the character to appear in bold as it gets twice as much ink.
Still, pagers like more/less do understand that format to mean bold, so roff, and that's still what roff does to output bold text.
Some man implementations would call roff in a way that those sequences are not used (or internally call col -b -p -x like in the case of the man-db implementation), and don't invoke a pager when they detect the output is not going to a terminal (so man bash | grep NAME would work there), but not yours.
You can use col -b to remove those sequences (there are other types (_ BS X) as well for underline).