Seems like the font being used by this Google's Easter Egg is not exactly the Comic Sans (because it's copyrighted) but something that resembles it.
If you zoom in, you'll notice some subtle differences. For example: the lowercase A is curved at its "tail" under Comic Sans, but it's a straight line under the Google's font. The "tails" of the uppercase S are also more "curved" under Comic Sans.
It's copyrighted to Microsoft Corporation. It only comes with Windows installations and with Microsoft Office installations, both of which aren't freeware as well.
While any person with access to a functional Windows installation could copy the files from C:/WINDOWS/Fonts, it doesn't mean that the file can be freely used legally, especially for embedding within the web, especially by another big tech corporation which Google is.
they can use CSS to force Comic Sans if installed.
Indeed (the CSS font fallback feature), but considering that the OP is using Google Search app, it's Android so it isn't expected to have the font (except if they manually installed the font using a file copied from a Windows installation) .