There is an argument that Google's search business is non-contestable
The article rightly points out that competitors don't provide results that are of the same quality as Google's, and that if they did, consumers would move to the alternate service. This is the argument for it being a contestable monopoly.
However, the quality of search is to a large part determined by the quantity of data available to the service, which is determined by the number of existing users. (The algorithms for generating search results are mostly documented in journal papers and implemented in open source software, so they are available to all players; there is some skill involved in creating the search engine from these, but quantity of data is a huge factor.)
The fact that the size of the existing userbase determines the quality of the product leads towards a search market with a single dominant player. So there is an argument that Google should be regulated as a monopoly (though probably not to the extent that a natural monopoly is).
You can see a similar thing with eBay and auctions: more buyers and sellers makes selling and buying respectively more attractive on that platform, and the market again tends towards a dominance by a single player.