Yes I believe that a person that studies English could become an Engineer. But being an Engineer requires experience and time. It's not like you'll pick it up in a day. On the other hand a person that studies CS or Engineering has learnt the basics and its easier for him to become one.
The way google is recruiting feels the right way for them (and for me) since they don't want to take in someone that has no idea and start teaching him on that.
Also if someone wants to work for a Tech Company like google I don't see why he will go study English... if English is what he likes best then why would he pursue working under a tech company.
I think you are trying to apply the logic that all the banks have that they'll hire whoever if he passes their tests. But they will train him into investments and guide them through. And also that person like everyone working on finance will have to undergo exams every-year to prove himself. (That's pretty much like studying finance if even more advanced).
Well Google doesn't want to go with the paragraph above.