Chickened out of a fullscale coup? Or just wanted to get some controls into place before confirming Morsi's victory? Or something entirely unsinister? We may find out yet, or we may never know...
If they did a full scale coup, there'd be blood on the streets. The important thing from SCAF's point of view is that they're going to control the drafting of the constitution, which means that they'll carve out whatever power they want for themselves. So there'll be a constitution, there'll be more elections, and a new Parliament, but it'll be on SCAF's terms.