Yes, scientists don't seem to realize that what apply to us humans is probably irrelevant to an alien race. I am pretty sure aliens might not need water or anything else we need to survive to actually survive.

Another example is absolute zero. -273C or 0 Kelvin is the temperature everything freeze and become inert. Pretty sure again that scientists only base themselves on us for this. The universe is big, there is probably things that thrive at that temperature somewhere.

Yeah for all we know there could be intelligent life out there with entirely different biology. Perhaps there are even chlorophyll based beings out there that live off photosynthesis.

I think part of it might be that it is just a good way to narrow down the search criteria, if we only look for what we KNOW can produce life, then we can direct our resources in less places with more chance (in theory) of finding something.