It is inconsistent with Android where the lines are not present and the background is transparent.

Workaround: 

<telerikChart:RadCartesianChart.Grid>
                <telerikChart:CartesianChartGrid x:Name="grid" StripLinesVisibility="None" />
</telerikChart:RadCartesianChart.Grid>

or:

chart.Grid = new CartesianChartGrid() { StripLinesVisibility = GridLineVisibility.None };

Available in the 2018 R2 SP release.