It was an accusation. Like, I'm not going to say his comments were good. They were stupid and divisive. But he was saying "well, if I went and traded favors with major corporations [implying this is what other politicians do] I'd raise more money than everyone else, but I'm not gonna do that." For some reason, people here are reading this as "well, if I went and traded favors with major corporations [wink wink I'm doing this] I'd raise so much money." And like, that's dumb.
Yes, it's really just a combination of boast and a fake appeal to morality - "I could out-fundraise Biden if I wanted, I'm just too ethical"; plus of course it also it is designed to foster this image of a man who's there for the common American rather than Wall Street, even if it's untrue.
He's also, of course, wrong. He's ten points behind in the polls. Big companies will not be handing huge sums off to an electoral campaign that increasingly looks doomed, because money only buys power if it backs the
winner. There's also the aspect of whether big business finds Trump sufficiently politically and economically disruptive that this outweighs his more business-friendly platform, on which I wouldn't like to say one way or another. Anyway, all he'd be getting is small donations by companies hedging their bets in case he pulls off an upset. Much more likely where they favour Republicans the money will be flowing into Congressional campaigns.