Those 2 images are entirely different resolutions (one low and the other much higher) so one was either exported at a higher resolution or it was larger size to begin with.
1x images WILL be pixelated because they are low res. 2x images will not be as pixelated because they are 2x the width and 2x the height (giving them 4x the total number of pixels).
In XD you should be designing at 1x and exporting for Web (Designed at 1x). This will give you 1x and 2x versions of your graphics.
Here's an article I wrote explaining 1x versus 2x in a general sense (it's not specific to XD, but the concepts can be applied to any app). I hope it helps. https://www.danrodney.com/blog/retina-web-graphics-explained-1x-versus-2x-low-res-versus-hi-res/
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