Isn't that in reference to a command literally named "login", presumably due to the lack of a good convention for separating words without the space character?
Like "useradd" on contemporary Linux.
That's very likely.
Re:The origin of “log in” (2011)
by raverbashing on Tuesday April 29, 2014 @06:38PM
(#7670386)
"the use of a wooden log tossed overboard attached to a knotted rope"
Now you know why speed is measured in knots
(Nowadays, it's a useful measure for great circle routes, that's why it's kept)
I knew about ships' logs, but I didn't know that the word "log" originated from the use of a wooden log tossed overboard attached to a knotted rope, so that the observed speed could be entered into a book that eventually came to be known as a ship's log.
Also interesting in that manual is that each "segment" of a command (what we now call a token) was six characters, blank-padded. The 7094 had 36-bit words and 6-bit bytes.
†http://bitsavers.trailing-edge.com/pdf/mit/ctss/CTSS_Program...
††http://webcache.googleusercontent.com/search?q=cache:SapGOxk...