PEI had a referendum on electoral reform back in 2016. The referendum ultimately resulted in MMRP, or Mixed Member Proportional Representation, getting 52% of the vote. However, PEI's premier. Wade McLauchlan refused to act on the results of the referendum because of the voter turnout rate was 36.46%. This pissed off a lot of voters, and so they've largely flocked to the Greens.Sounds about right, given how low the Liberals' numbers are in that poll (not to mention the NDP, but then again the NDP wasn't historically that popular throughout much of Atlantic Canada). But I'm guessing it's the habitual Liberal (either actual Liberals or Swing) voters that wouldn't have been able to bring themselves to vote Conservative instead - something something Stop Harper - and they're pissed enough at the NDP that their 'only' option is the Greens.
The other option is that the pollsters want to make the Greens look more viable than they actually are by sampling a hippie commune. Because reasons.