From 2008 through 2018, the GSS surveyed 814 non-citizens living in the US. Eighteen of those 814, or 2.2%, reported voting in a US presidential election during that time. The number who would have been legally permitted to have done so would of course be zero.
Maybe it’s transcription error, maybe it’s respondent confusion over voting in local contests in jurisdictions not requiring US citizenship to participate in lower level elections, maybe it’s trolls yanking interviewers’ chains–or maybe non-citizen voter fraud is a real thing.
GSS variables used: USCITZN(2), YEAR(2008-2018), PRES04, PRES08, PRES12, PRES16