How could you make a by-election to fill one vacancy proportional without changing the entire voting system?

Cromarty Firth (Highland) by-election, most popular second preference by party:

SNP <-> Alba
Ind RC <-> Ind MR
Reform UK -> Ind RC
Lib Dem -> Ind RC
Green -> SNP
Labour -> Lib Dem
Conservative -> Ind RC

Genuine question: FON Poll showed 2% in Const and 7% in List for Alba. I think you’d accept that 2% for Const is largely accurate given results in GE. How can one be accurate and the other not when the same people are asked?