The casualty count is pretty easy to explain. First, that Wikipedia piece is doesn't really tell the whole story. The actual force that hit Thornton's men wasn't that large - some of the 700 to 1000 having been detached for other jobs. Then, if you figure that Thornton's Cav got the heck out of there pretty quickly on hearing the gunfire at and of the pickets, it isn't really surprising that it was so low. The gentlemen who told us the story of the engagement said that the pickets were half a mile or more from the main body. So even if the Federals did have that 1000 men, you can't shoot who ain't there.
I'm way the heck up in Lake Co. almost 3 hours from San Ramon, but thanks for the offer. I take it you are in S Calif?