That's great! I'm so glad Mathew got some extra fun out of his veg! Hanging upside down is a pretty natural position for a lorikeet - Lilly even hangs herself upside down from the bars of her cage when she's lapping up her wet mix rather than just standing on a perch or the side of the dish, so it would seem to be their preference.
As far as the dry nectar powder is concerned, it may just be a case of trying different brands before you find one that Mathew likes. There are a couple of brands that Lilly won't touch, but one that she absolutely loves, so it's worth perhaps experimenting with some different manufacturers. Same with other parrot species and pellets really, some like Harrisons, some like Tops or Roudybush, it all comes down to individual preference. I'm not personally sure about bee pollen though. Lorikeets in the wild do eat pollen from native flowers and I've used it as an additive to Lilly's dry mix but have never used it exclusively. I'm not sure that I would to be honest. Living in Australia I provide Lilly with natural, native blossoms for forage almost every day so she would get some pollen that way. But I will try to remember to ask my bird vet about it next time I see him
Just for a bit of fun I've attached a (very short) video of Lilly attacking her bunches of broccolini that I suspended from the roof of her cage for her ...
Unfortunately the lighting is bad because it was so bright outside, and it's only short because every time I aim the camera at her she'd much prefer to come over and jump on me to investigate it instead, but you get the idea of how much she enjoys climbing up and around her veg rather than just having a dish of food presented to her. I hope maybe you can get a video of Mathew enjoying his greens too, I'd love to see it!