Yes I realise that now, but stupidly :
I presumed Google was a reliable source.
Google does not send people emails. I believe that if you checked the coding in that email message you would discover that it was not actually from Google at all, and the download link for whatever it was you downloaded wasn't legit either. If you had been on a Windows machine, you'd be screwed right now, but luckily you're on a Mac.
Is the updated Safari version not developed in collaboration with Apple?
Again, very VERY unlikely to be an actual download of Safari from Apple.
Are there no safeguards built into macs to reject updated software recommended to be used on Mac?
There are ... on modern Macs.
How should I have proceeded ?
All Apple software updates (like Safari, ie things made by Apple) are handled through Software Update. There is no other channel you should be using for updates except for third-party software, and for that you can check with the vendor's own website.
NEVER click on a link in an email that came from someone you don't personally know, particularly anything purporting to be your bank, brokerage, a vendor you like, a company you do business with, a company you don't think you've ever done business with -- and especially not if the message is trying to scare you in some way ("your account will be deleted/frozen," that sort of thing). Just ignore/trash such emails. If you have a concern, call the business or visit their website independently and see if anything's amiss. Most of the time, such scams give themselves away through their poor use of the English language.