Happens all the time. Are you sure you didn't subconcisely pick up something? I have found myself doing that PLENTY of times. In Nashville where you hear a thousand songs every few days, it is very easy to subconsiously pick things up.
I was even writing with a number one songwriter one time and we wrote a pretty cool song. we were about ready to demo it and about two days later he calls me and says "Man, we have to stop that one now.' There was another one out JUST like it. Particularly if there are songs that are many years back. I constantly get someone in Nashville doing one of my workshops that have a song that is exactly like some big hit back in the years gone by. You say something to them and they FREAK! they didn;t even think of it. And once you mention it they realize it and feel pretty dumb.
There are only 12 notes and only so many ways to say "I love you." So you are going to overlap. It is like that Richard Dryfuss line from the original "Jaw's movie." "A shark is attracted to the specific type of sound a swimmer makes when they go into the water. You cannot avoid it."
"A songwriter is attracted to the EXACT sound of music they are attracted to. and their are only so many notes. You cannot avoid it."

MAB