I think I remember other tests that ranked it a bit heavier, but ESET felt very light on my system when I was trying it out. There were no real major system slowdowns or hiccups.You're comparing lightness with ram usage only which is wrong. There are many other parameters beside ram usage.
AV-Comparative does an excellent job at testing this. Check this: Performance Test April 2019
ESET is the lightest in their test as well so my and many other user's personal experience + this result surely verifies it.