cats meet - confusing

Hi

I let the cats out for a supervised meeting today, and I was a little
confused as to what happened. They have been separated for almost 2
weeks now. I have been switching them around a few times a day, and
letting them see each other for short sessions. They are eating with
their dishes touching the gate with no problems as well. I also have a
Feliway diffuser I plugged in yesterday to help things out.
The meeting started by Elwood, the 5 month old kitten, charging at Jake,
who is the older, and bigger new cat. They patted each other a few
times, and it looked like they were going to start playing. Elwood then
tried grabbing Jake and giving him a big ol' hug.
Then it seemed to me like Jake started to get nervous and more serious,
and started biting at Elwood's neck. He got Elwood down on his back, but
he didn't quit biting his neck. This is where I got worried, and broke
them up. It was very difficult for me to tell if they were playing or
fighting for real. I didn't want Jake to hurt Elwood.

I am wondering if this is normal? Did I mess things up by breaking them
up? Should I have let them go at it? They weren't hissing or growling
that I noticed if that helps.

It seems to me like Elwood makes Jake very nervous, which is strange
because he seemed to have the upper hand. Can anyone explain this?

Thanks!

Justin