Do you mean a new page that didn't previously exist, or just a new request? When the googlebot picks up images or css-- whether or not there's a referer-- it always starts with the html. No referer for the page, ever.
Incidentally I have just-- don't everyone yawn at once-- come upon an MSNbot doing the same thing. From the ordinary bing/msn 207.46 range, using one of those MSNbots that wear street clothes with too many spaces. I've seen it before trying to get at piwik files but this is the first time I've observed it going for a css file. Quick detour to raw logs tells me that it, too, has been doing it since at least April, though only with css files. Again, that's with a referer, always coming immediately after a request for the html itself.