What's the difference? The only difference is semantic, we seem to have defined "swimming" to be arbitrarily restrictive (as in, only applying to animals), while we haven't done so for flying.
Meanwhile, we can say a magnet is attracted to metal, and no one says "wait, it can't ACTUALLY be attracted to it, since that takes a brain and sentience and preferences."
And then, most of us don't bat an eye if someone says "my computer thinks the network is down" or "my phone doesn't recognize my face" or even "the heater blowing on the thermostat is making it think it is hotter than it is." It's not helpful to interject with, "well, thermostats don't really think."
The point is, these are arbitrary choices of how we define words (which may vary in different languages), and they aren't saying meaningful things about reality.
Not sure what he meant by that, it doesn't really make sense to me: thinking yields information and deductions that can be very useful, while swimming by itself accomplishes nothing useful.
Actually, I just can't make any sense of the sentence, because while I have a general idea of what a thinking machine could be, I have no clue what it means for a submarine to "swim", versus whatever the alternative is ("self-propelling"?).