NZX's 7.22% is calculated as the last year's interim & final dividends (cash + imputation credits) of 20.83c & 33.33c respectively = 54.16c on sp of $7.50 = Gross Div Yield 7.22%
https://www.nzx.com/instruments/HLG/dividends
For the next financial year, you will have to make your own estimate of what the final dividend is going to be to get the gross dividend yield.
If one takes a simplistic view that the final dividend will be 15% more like this interim dividend (23c vs 20c), then the prospective gross yield for F21 will be 8.2%.
I note that HLG is only paying out 70%* of EPS of 33c with this interim dividend of 23c when the company could have easily paid out (like previous years) 30c
so I am picking a bumper 30c final dividend.
So I am calling it 9.8% gross yield for F21.
*HLG is right to be cautious (like in 2020) with the pandemic still out there and lockdowns being a possibility until everyone who wants to get vaccinated, gets vaccinated.