I think it's more accurate to say that autistic people tend to express their emotions
much more intensly than non-autistic people, when they do decide to express them. Most non-autistic people will tend to consider social norms because they innately understand to not disrupt them. Autistic people, especially when they've decided on something, are completely willing to eschew social norms to right a wrong or express their stance or something similar.
That's not to say they're more or less empathic than others, that's just as variable as with non-autistic people (basically just because you're autistic doesn't mean you're incapable of being an asshole). However because autism partially includes a stunted social growth, the decision making process that might prevent a normal person from say, commenting on someone being rude in public (ie. Not causing a fuss, not wanting the attention to be focused on them) just... isn't quite there. That can both be good and bad depending on the situation.
At least that's been my experience having been a cashier (a couple years ago now) and having had customers who were really obviously autistic. They tended to lean towards being really expressive/opinionated, just... not especially caring if expressing that opinion is appropriate. That can be amazing if you're dealing with an especially frustrating Karen who tries to haggle prices in a fucking supermarket because she didn't bring enough cash (no cashier wants to risk putting their foot down and that blowing up in their face but in supermarkets you do not haggle the total, it's just not a thing), so having another customer back you up feels very solid/helps when management inevitably has to be called. And it can equally be frustrating when they start counting out the VAT that the cashiers computer calculates and they decide the rounding isn't to their liking/when they figure out there's a discount on a product and it isn't applied and then they try to get the cashier to correct it instead of customer service.