Safari for Windows came out in summer of 2007, Google Chrome came out in September of 2008. Granted Chrome development started in 2006ish which was probably around the time Safari for Windows started. By the time Safari for windows was released those in the WebKit community knew Google was up to something, but didn't know a timetable, any details etc and from discussions they tossed out the first version so when Safari for Windows was released perhaps Google Chrome as we know it today was just starting. Looking at it from a business perspective or even just a 2006 perspective Apple's move makes a lot of sense.

Edit: Some of my memories are a bit fuzzy about what was going on exactly when in relation to everything else so feel free to correct any mistakes in the above.