IME this is not true. A month ago I had a 7" IT and 5" NGT and they went at it all the time. I had to get rid of the IT because it constantly chased after my NGT. I tried to keep them full most of the time but that didnt help noticeably.
Now my ngt owns the left corner of my tank. None of my baby IT's or even my bigger NTT's can venture to the left side without a charge from the ngt. No real damages to any fish tho, just some chasing and fin nipping at worst.