I had a look on their
website and couldn't work out where this ParlGov survey was supposed to be from (they seem to focus just on election outcomes, though do have a function for assessing parties' positions on the political compass), but
did find a reference to a survey of 15 Western nations in
this study, which also references ParlGov, seems to be covering the same subject matter and is based on analysing the 2016 European Social Survey (
pdf) data. I'm wondering if he got his reference muddled.