(replying to everyone)
(Rick)
"uname -r" will show you the currently running kernel:
(Joe)
uname -r
I get:
-----
bash.1[~]: uname -r
4.16.13-200.fc27.x86_64
bash.2[~]:
-----
That matched the dnf log line, so apparently the update was successful;
this is not a real problem.
(Tom)
This has been happening for a while:
https://bugzilla.redhat.com/show_bug.cgi?id=1497444
The bugzilla says it is fixed, but I guess not in f27.
In comment 17, Russell notes that the "plumbing" problem still occurs.
This bug is "CLOSED RAWHIDE", but another bug was needed (1535458), and
it's still in state "NEW".
Thank-you everyone for the help.