sure being in that small an environment will have some impact on its overall size. however it will not stop it growing too big for the tank,
you need a BIG tank for arowana, personally I do not feel it is fair to keep these species overall, as with red tail catfish, these are fish that grow much larger than almost all fishkeepers can give adequate space to.
when you have tropical ponds (20' long +) then you start getting near to the spaces that these sorts of fish will appreciate. IMO fish need a MINIMUM of 6 times their body length to swim in, and preferably more (most of my sp have 12times)
before you buy it, consider living the rest of your life in a telephone box, would you be happy to just survive...