Can this even be considered a free speech issue? They aren't deleting his tweet, only displaying it alongside a fact check. Of course you can try to call into question the impartiality of the fact check but that is a long way from not deciding not to show the content.
A fact check would be fine if it led to objective analyses of some sort, or even Wikipedia. But when I clicked it, it displayed some highly partisan sources, including a CNN article with its usual "Trump bad" vitriol. Maybe it was an algorithm's fault, but it didn't work at all.
In which alternative universe is Wikipedia objective? From my experience it is far-left, sometimes deliberately spreading fake news if it fits their narrative. This is especially visible in articles about politicians and historical events.