http://onion.to/ is a proxy into Tor hidden services.

This gateway to Tor hidden services provides convenient access to Tor hidden services. It is a pure proxy that forwards requests to the respective hidden service. We do not store any data and are not liable for the content.

As you can see from the domain, it does not end in .onion as the hidden service domain inside the Tor network does. In fact the hidden service domain

foo.onion

is mapped to

foo.onion.to

which can be accessed via normal HTTP without using a Tor client. This provides no anonymity:

Onion.to as a gateway cannot offer any anonymity for the visitor.

Google can access such a proxied hidden service without using a Tor client, too.