The Ivory Coast international, who joined from Vitesse Arnhem in the summer, began slowly in south Wales but has now hit his straps in the absence of injured forward Michu.
Bony's two goals in the weekend's 4-3 loss at Liverpool took his Premier League season tally to 10 from 23 appearances for a total of 19 in all competitions which has delighted his skipper.
"We had Michu's goals last season but he has been out for a while and Bony has stepped up for us," Williams told the club's official website ahead of Thursday's Europa League clash with Napoli.
"I think confidence is a big thing, particularly for strikers, and you can see the confidence he is playing with.
"We love him and he is involved in the build-up a lot more now. The main thing is confidence and he's getting that from finishing his chances."
Williams added: "It is not just his goals. During the last few weeks I have really felt sorry for the opposition defenders as he has been unplayable.
"He's got to be the strongest player in the league but he uses his strength and body well. His strength is obvious but his touch and his awareness have been excellent too. He is on fire at the moment."
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