If a bag is too long to fit in the overhead bin lengthwise (i.e. wheels first for roller bag), then it's very likely it's taller than the sizer dimensions. Just because a gate agent didn't stop you doesn't mean your bag meets the regulations.
It's annoying when someone has an oversized bag and stores it douche-bag style, taking up the full bin. Overhead bin space is already at a premium on the 319. I'd expect the other paz who may have also paid good money for their Z fares may be frustrated to find that there are only 4 bins for 8 pax, and it sounds like one bag is likely taking up the better part of a full bin.