I had heard he slept elsewhere, but not the part about a Pentagon official picking him up. If you find the answer to your question, please ping me.
I read it here about him sleeping at a Pentagon official home.
I saw a post about a picture of Kerry and Ted Kennedy. The poster said that the caption under the picture stated that the two were discussing whether or not Kerry should risk sleeping in the park and getting arrested. I guess he decided not to, and Kennedy probably helped him out.