Yes, I looked at the numbers this morning. Trump won 451,905 votes, Haley 298,047, but a total of 303,895 votes went for a candidate other than Trump. South Carolina isn't the reddest of Red states, but it's up there, and majority Republican. As you say, the question is: how many were voting FOR her, and how many firmly against Trump? Around 4,000 "threw" their votes away to De Santis, Ramawamy, Christie and others. IMO, those are protest votes against Trump.
This is anecdotal, but I heard a SC woman yesterday to say that she liked Haley a lot, and was voting for her. That she had voted for Trump before, but she has grandkids and thinks he's a terrible influence. That if it's Trump or Biden in the general election, she'll vote for Biden. One does wonder how many Republicans out there just can't stand with Trump anymore? A lot of "regular Republicans" were put off by Jan. 6th. Others can't abide the legal issues.
Haley is committed to staying in, at least until Super Tuesday, and she has the money. (Ask yourself where THAT money comes from...Never Trumpers, I'd bet.) Whether it's her strategy for down-the-road, or her patriotic commitment to blocking Trump, or some combination, she will be a thorn in the side of the Trump campaign if she keeps exposing his weakness by doing well-enough to show how many won't vote for Trump, at least for now.
According to what I've read, at around 25%, this is a high voter turnout for a primary. Given that it wasn't predicted to be close, you have to think that a lot of folks turned out to vote against Trump. Now, whether they'll hold their noses and vote Republican in the general election, vote for Biden, or just stay home is yet to be seen. But, by comparison, in a completely uncontested Democratic primary in SC, only 5% voted. Obviously, a lot of voters who don't want Trump came out. It can't all be a Haley local wave. I agree with you that the Trump campaign is surely quietly panicking behind the scenes.