I haven't seen anything like this on my phone, Maybe my google keyboard is not yet updated, Well I really think Bitcoin is very well known by Google and many people are using the word bitcoin that is why I think Google added it, In this aspect, we can really see that Bitcoin is very popular and many people are getting to know more about it and accepting it, And Google is innovating it to the fullest.
Man OP was very specific about the particular device with you can found the Bitcoin logo on the Google keyboard and he didn't not said on all devices that uses Google keyboard. Except if you are using iOS as op rightly said then you need to update your Google keyboard.