HOV is up 9%, possibly because short sellers don't want to be in this market, and they don't want to be against Buffet's bet, says Jon C. Ogg at MarketWatch. Hovnanian has a connection to the California and Florida housing markets, which are especially volatile, so anything is possible.
As for XHB, this small shot upward isn't really a big deal; it doesn't change anything. XHB is down 16.9% for the year, so hopefully it can only get better from here. Berkshire Hathaway already owns a lot within the housing sector, so it would be easy to integrate HOV. Imagine what can happen for this sector if it's already up based on rumors and short covering.
XHB vs. HOV 1-yr chart: