Good question -- I believe the source is here: https://www.bruegel.org/analysis/european-unions-remarkable-...

Reading between the lines, I do not think it distinguishes between full-time and part-time employment: "In Europe, employees tend to work fewer hours than in the US, partly because there are more paid holidays, the typical working week of a full-time employee is shorter and there is a larger share of part-time workers than in the US."