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, 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).